It is well-established that the availability of a prior art reference is dependent on the "effective filing date" of a patent or patent application. Any practitioner seeking to invalidate a patent knows that the ideal references used both for prior art and for demonstrating the knowledge of a POSITA will have been made public before the effective filing date of the patent in question. After all, what better way is there to prove that a person of ordinary skill in the art would have known of some technological development before a particular date than to point to a description of that technological development that was available to the general public before that date?
However, while the ideal reference may be made public before the filing date of a patent, pre-AIA 35 U.S.C. § 102 (e) (and AIA 35 U.S.C. § 102(a)(2)) allows for certain international or US patent publications or patents to be used as prior art as of their own filing date, at least for purposes of an obviousness analysis. The question remains whether demonstrating the knowledge of a POSITA follows the § 102 (e) rule allowing for a filing date to substitute for date of publication or accessibility to the public. Specifically, there is yet a question of whether references filed before but published after a patent's priority date can be used to show what would be known by a POSITA at the time of invention.
In a recent decision in the Northern District of West Virginia, Chief Judge Thomas discussed exactly this issue when denying a Motion for Preliminary Injunction. In re Aflibercept Patent Litigation, Case. No. 1:24-MD-3103, N.S.W.V. (Sept. 23, 2024). In an interesting turn of events, the patent challenger attempted to use a patent publication not as a piece of prior art used to invalidate the challenged patent, but as evidence of how a person of ordinary skill in the art would have interpreted the claim language. Id. at 66-69. The reference in question was filed eight days before the challenged patent was filed and was published several months afterward. Id. Thus, the particular issue that was presented was whether a reference that was filed early enough to be used as a prior art reference to invalidate a patent could be excluded from use as evidence of the knowledge of a POSITA at the time of filing when conducting a claim construction analysis.
In coming to the conclusion that evidence of the knowledge of a POSITA must come from a source available to the public before the effective filing date of the patent in question, the Aflibercept Court started by looking at Phillips, which says that "the ordinary and customary meaning of a claim term is the meaning that the term would have to a person of ordinary skill in the art in question at the time of the invention, i.e., as of the effective filing date of the patent application." Phillips v. AWH Corp., 415 F.3d 1303, 1313 (Fed. Cir. 2005) (en banc) (emphasis added).
The Court in Aflibercept then examined a few other cases to come to the conclusion that the only evidence that could be used to determine a POSITA's understanding of a claim term at time of filing had to not only be in existence but also be available to the public at the time of filing. In its analysis, the Court pointed to several cases that did not allow outside sources to provide enabling disclosure where there was not enough disclosure in a patent in question. See Kopykake Enters., Inc. v. Lucks Co., 264 F.3d 1377, 1383 (Fed. Cir. 2001) ("when a claim term understood to have a narrow meaning when the application is filed later acquires a broader definition, the literal scope of the term is limited to what it was understood to mean at the time of filing."); Schering Corp., 222 F.3d 1347, 1353-54 (Fed. Cir. 2000) (holding that claims must be construed "at the time of filing," based on support in the specification, and that it is impermissible to "enlarge the scope of the patent to embrace technology arising after.").
The Aflibercept Court then discussed a case from 1974, In re Glass, to analyze more squarely the distinction between uses of prior art for different concepts in patent law. In re Glass involved the question of enablement and stated that "as a matter of common sense, it is clear that the contents of a patent application which may be available as 'prior art' under § 102(e) to show that another was the first inventor may not have been known to anyone other than the inventor, his attorney, and the Patent Office examiner, and perhaps the assignee." In re Glass, 492 F.2d 1228, 1231-32 (C.C.P.A. 1974). Specifically, the court there found a distinction between determining the status of prior art (§ 102 (e)) and filling in potential deficiencies in the enablement requirement (§ 112). The reasoning went that using additional details to get to sufficient disclosure for enablement suggests there may have been an incomplete invention at the time of filing.
Aflibercept examines the potential to use later prior art to construe claim language, given a footnote in In re Glass that suggests there are instances where a later published reference can be used, before stating that, "[t]hat footnote, however, does not specifically address secret prior art but rather discusses indefiniteness (35 U.S.C. § 112, second paragraph), which is not at issue here. Cases decided after In re Glass makes clear that references available to the POSA only after the date of invention (or effective filing date) should not be relied upon for establishing what was generally known to a POSA. Phillips, 415 F.3d at 1313 (noting claims are to be construed based on the understanding of a person of ordinary skill in the art "at the time of the invention")." Aflibercept, 1:24-MD-3103 at 68, n.23. The argument is that "secret prior art," which can be used generally to invalidate a patent or help show definiteness, cannot be used to show what was known to a person skilled in the art since it was not "known to anyone other than the inventor, his attorney, and the Patent Office examiner[.]" In re Glass, 492 F.2d at 1231-32.
In Aflibercept, the Court essentially decided that, when it comes to priority dates and prior art, claim construction falls under the same umbrella as enablement, in that both focus specifically on what is known to a POSITA at the time of filing of the invention. The logic follows the idea that both are about understanding what a claim entails. Definiteness, they seem to say, is about the bounds of the claim, about telling a POSITA what the bounds of the claim are rather than explaining what the claim terms mean. Possibly, claim construction is more about filling in gaps, like enabling disclosure.
Here, the Court analyzed the language of the law, holding to the idea that a POSITA cannot know what is not disclosed to the public. Whether this distinction holds water given that the idea of an obviousness analysis, while partially about who got to the patent filing first, in theory still assumes some level of a POSITA's knowledge at the date of an earlier filed patent, is up for debate. And there is an interesting dividing line here that allows a reference to be used as a secondary or tertiary reference in combination but does not allow the same disclosure to color the understanding of the claims.
Policy considerations can push this analysis either way. On the one hand, following § 102 (e) for adding to the knowledge of a POSITA with regard to claim construction creates a consistency with a prior art analysis. It further follows the logic that suggests there may be some lag time between when a technology is known and when such knowledge is officially published. Besides, insofar as a later publication does not seek to expand the meaning of a claim term but rather to clarify what it would have meant, the fact that such a definition or clarification was recorded somewhere, even if not yet made public, may shed light on what may have been understood at the time of filing.
On the other hand, requiring publication for showing what a POSITA would have understood a term to mean at the time of filing may provide incentive for patent owners to be clearer when drafting their applications. The distinction between the timing for § 102 (e) and claim construction may be justified by the distinction between the battle to get to an invention first and the need to interpret claims as they would be understood to mean by the inventor of the patent in question. Insofar as the quid pro quo of patent rights centers on disclosure of an invention to the public, drawing the line for what references can be used for claim construction at what was known to the public may further that goal by encouraging patent drafters to spell out what a claim term means rather than relying on the understanding of a POSITA, which may potentially shift over time. Also, the analysis for including a reference as prior art requires more work to prove such use is appropriate, including showing a motivation to combine, which may justify allowing the reliance on the earlier filing date.
For now, this decision is a reminder to all who seek to challenge a patent that the safest references, even if they are not part of a combination, are disclosed to the public before the filing date of the patent. This further serves as a warning that relying on "secret prior art," while allowed for an obviousness analysis, may not work for claim construction. This decision may also serve as a reminder to those drafting patents to be clear in their definitions and to not rely too heavily on filing in gaps with external knowledge of a POSITA since such definitions may change in unexpected ways over time, leaving evidentiary problems that could easily be resolved through clearer drafting.
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