While the recent changes to a first to file system have been applicable for several years, many pending applications still fall under pre-AIA rules where an inventor can swear behind a reference that would otherwise qualify as prior art.
Swearing behind a reference, such as via a Rule 131 affidavit, generally requires that one have some evidence of prior invention and diligence. While an invention disclosure form or inventor notebook is a traditional type of evidence in this situation, there is another avenue that can be very helpful to an application. That alternative avenue relates to using drafts of a patent application as evidence of prior invention.
A draft patent application is often much more attractive for swearing behind a reference since it usually has language that matches pending claims, meaning that it is strong evidence of all of the claimed elements. Whereas a notebook may have general concepts, a draft patent application usually has detailed language and sample claims that are hopefully close to the currently pending claims (which may have been amended to avoid other prior art applied by the USPTO).
One example illustrating how to navigate through the issues in this situation is US SN 12/357,078. The Applicant in this application, WMS Gaming, used a draft application prepared by patent counsel to swear behind a prior art reference. The Examiner failed to accept the draft application and the Applicant appealed to the PTAB. The PTAB confirmed that a draft patent application is perfectly acceptable for showing prior invention. The issue in this case was whether the draft application showed possession of the claimed invention. The PTAB explained that the specification provided sufficient disclosure because it disclosed the claimed features as one possibly way of achieving the desired results, and it was not necessary that it disclose the claimed features verbatim.
So, for cases falling under pre-AIA rules, if the cited reference can be antedated by a draft application that supports the claimed features, consider filing a Rule 131 declaration and supporting evidence of diligence to remove the reference.