In certain circumstances, references cited to show a universal fact need not be available as prior art before applicant’s filing date. In re Wilson, 311 F.2d 266, 135 USPQ 442 (CCPA 1962). Such facts include the characteristics and properties of a material or a scientific truism. Some specific examples in which later publications showing factual evidence can be cited include situations where the facts shown in the reference are evidence “that, as of an application’s filing date, undue experimentation would have been required, In re Corneil, 347 F.2d 563, 568, 145 USPQ 702, 705 (CCPA 1965), or that a parameter absent from the claims was or was not critical, In re Rainer, 305 F.2d 505, 507 n.3, 134 USPQ 343, 345 n.3 (CCPA 1962), or that a statement in the specification was inaccurate, In reMarzocchi, 439 F.2d 220, 223 n.4, 169 USPQ 367, 370 n.4 (CCPA 1971), or that the invention was inoperative or lacked utility, In re Langer, 503 F.2d 1380, 1391, 183 USPQ 288, 297 (CCPA 1974), or that a claim was indefinite, In re Glass, 492 F.2d 1228,1232 n.6, 181 USPQ 31, 34 n.6 (CCPA 1974), or that characteristics of prior art products were known, In re Wilson, 311 F.2d 266, 135 USPQ 442 (CCPA 1962).” In re Koller, 613 F.2d 819, 824 n.5, 204 USPQ 702, 706 n.5 (CCPA 1980) (quoting In re Hogan, 559 F.2d 595, 605 n.17, 194 USPQ 527, 537 n.17 (CCPA 1977) (emphasis in original)). See also Amgen Inc. v. Sanofi, 872 F.3d 1367, 1375, 124 USPQ2d 1354, 1359 (Fed. Cir. 2017)(post-effective-filing-date evidence could be relied upon to show that patent failed to disclose a representative number of species of a claimed genus, and to show that patentees may have engaged in undue experimentation as of the effective filing date to enable the full scope of the claims). However, it is impermissible to use a later factual reference showing the state of the art existing after the effective filing date of the application to determine whether the application is enabled or described as required under 35 U.S.C. 112(a) or pre-AIA 35 U.S.C. 112, first paragraph. In re Koller, 613 F.2d 819, 823 n. 5, 204 USPQ 702, 706 n.5 (CCPA 1980). Post-effective-filing-date evidence offered to illuminate the post-effective-filing-date state of the art is improper. Amgen, 872 F.3d at 1374, 124 USPQ2d at 1359. References which do not qualify as prior art because they postdate the claimed invention may be relied upon to show the level of ordinary skill in the art at or around the time the invention was made. Ex parte Erlich, 22 USPQ 1463 (Bd. Pat. App. & Inter. 1992).
IN SOME CIRCUMSTANCES A FACTUAL REFERENCE NEED NOT ANTEDATE THE FILING DATE