Burden of Proof on Sufficiency of Disclosure – Does it automatically shift between instances at the EPO?

Case Law | 17.01.2024

Sufficiency of disclosure or the lack thereof is a ground of opposition before the EPO and thus often one major battleground in EPO opposition proceedings, in particular for patents where compositions and parameters are claimed. Perhaps more than for other grounds of opposition, the issue of proof in substance is an important one when it comes to insufficiency. Normally, attacks succeed if the Opponent can raise serious doubts supported by verifiable facts and evidence that a patented invention is insufficiently disclosed, i.e., cannot be performed by the skilled practitioner without undue burden and inventive activity. Such verifiable facts and evidence can be the Opponent’s own experimental data derived from unsuccessfully trying to re-work the claimed invention, but also technical arguments occasionally suffice. The burden of proof may however shift to the Proprietor, if the attack by the Opponent has shaken the presumption of sufficiency inherent in a granted claim. Hence, whenever insufficient disclosure is discussed, it is very important to know who carries the burden of proof on the substance and thus needs to submit respective evidence or arguments.

HOFFMANN EITLE’s Munich partners Christopher Furlong and Michael Müller were defending an alloy patent in EPO appeal proceedings T 1076/21 and were faced with an interesting situation. The patent in question had been revoked by the Opposition Division for lack of sufficient disclosure, which was the subject of the Appeal proceedings. The Opponent argued that the burden of proof that the patented invention is sufficiently disclosed was shifted to the Proprietor for the reason that the Opposition Division found a lack of sufficient disclosure and thus revoked the patent. Hence, the Opponent saw no need to provide (further) evidence for insufficiency at the beginning of the appeal proceedings. Their later filed evidence was then rejected by the Board.

Notably, the Board dealt with this issue in quite some detail and found that the burden of proof regarding the facts, arguments and evidence on the substance (which initially lies with the Opponent) does not shift to the Proprietor just because the patent has been revoked due to an alleged insufficient disclosure. In addition, the Board explained that it is down to the Proprietor to substantiate on appeal why that decision is wrong. The burden of proof on the substance (and in consequence the benefit of the doubt), however, is only shifted when the Opposition Division's assessment that the presented facts, arguments and evidence were sufficient to discharge the Opponent's burden of proof turns out to be correct. The Board clearly distinguished between the “burden to substantiate” and the “burden of proof on the substance”. If a patent is revoked due to a lack of sufficient disclosure, the Proprietor has the burden to substantiate on appeal why the decision of the Opposition Division was wrong. However, the burden of proof to show that the patented invention is actually sufficiently disclosed does not automatically shift to the Proprietor in such cases.

The decision of the Board is reasonable and pragmatic from a Proprietor’s perspective. If there would be an automatic shift in the burden of proof on the substance following revocation based on a lack of sufficient disclosure, the Proprietor would face high extra efforts when entering the appeal stage trying to prove sufficiency. From an Opponent’s perspective, the decision advises caution in that one cannot rely on a favourable decision of the Opposition Division, and assume that it is up to the Proprietor to prove sufficiency in the appeal stage. Instead, Opponents are advised to review the strength of their first instance presentation on lack of sufficient disclosure and consider filing further evidence as early as possible in the appeal stage where they consider this necessary.