Which statement is true regarding prior use before the filing date?

Establishing prior use before the filing date can serve as a defense against a claim of patent infringement. This defense is grounded in the legal principle of prior use rights, which allows a party to argue that they were using the invention before the patent was filed. If the accused infringer can demonstrate that they were practicing the invention prior to the effective filing date of the patent, they may avoid liability for infringement based on that prior use.

The understanding rests on the nature of patents, where the rights granted by a patent do not extend to activities that predate the patent's filing. Therefore, if an individual or entity can show that they were using the patented invention prior to its patenting, they can leverage this as a critical component of their defense strategy. This principle underscores the importance of documenting prior use in the context of patent law.

The other options do not accurately capture the implications of prior use. While prior use may affect the validity of a patent in certain situations, it does not automatically invalidate the patent itself. It's not universally accepted as prior art, and it certainly isn’t limited to use only in litigation. The nuances of its application demonstrate the significance of prior use in defending against patent claims.