c) Sufficiency of disclosure 

The burden of establishing insufficiency of disclosure generally lies with the opponent. See also chapter II.C.6.8 and II.C.7.2 on how this applies in the context of medical uses, and G 2/21 (OJ 2023, A85), points 74 and 77 of the Reasons.

In T 1076/21 the board set out how the burden of proof is to be allocated on appeal following revocation of the patent by the opposition division (see Catchword and the detailed account of T 1076/21 in chapter II.C.9.1). It made it clear that, after a decision by the opposition division allowing an objection of insufficiency, it was down to the patent proprietor to substantiate on appeal why that decision was wrong. However, the burden of proof on the substance (and in consequence the benefit of the doubt) only shifted if the opposition division's assessment that the presented facts, arguments and evidence were sufficient to discharge the opponent's burden of proof turned out to be correct. Referring to the case law, the board in T 1076/21 also stated that the initial burden on the opponent to provide facts, arguments and evidence for an assertion of an insufficient disclosure could shift to the patent proprietor once the opponent had successfully discharged its burden of proof by submitting sufficient facts, arguments and evidence to rebut the presumption of sufficiency (T 338/10, T 2218/16). However, this shift could only be caused by sufficient submissions on the substance; formal reasons alone, such as the mere existence of the opposition division's decision to revoke the patent, did not lead to a shift of the burden of proof on the substance. If the reasoning in the impugned decision as such was found to be wrong, there could not be any shift of the "burden of proof on the substance" (T 499/00, T 1608/13). T 585/92 had merely stated that the appellant bore the burden of substantiating the appeal. It did not imply that the decision under appeal reversed the burden of proof on the substance.

In T 63/06 the board explained that, once a patent had been granted, there was a presumption that it was valid. The weight of submissions required to rebut this presumption depended on its strength. The board then distinguished between two cases. A "strong presumption" existed where the patent contained detailed information on how to put the invention into practice, including test results relating to a particular property. In such a case, detailed information or evidence, e.g. in the form of comparative tests, was required to establish a lack of sufficiency (T 63/06, point 3.3.1(a) of the Reasons). By contrast, when the patent did not give any information on how a feature of the invention could be put into practice, there was only a weak presumption that the invention was sufficiently disclosed. In such a case, the opponent could discharge the burden of proof by plausibly arguing that common general knowledge would not enable the skilled person to put this feature into practice. The patent proprietor then bore the burden of establishing the contrary assertion that common general knowledge would indeed enable the skilled person to carry out the invention (T 63/06; summary of this case law in, for example, T 338/10, T 518/10, T 347/15 and T 1889/15; systemised approach in T 1076/21).

In T 480/11, T 1529/17 and T 518/10 the boards were of the opinion that the opponents had discharged their burden of proof on the substance by submitting experimental data. In T 188/18 the board concluded that the opponent had discharged its burden of proof on the substance not by submitting experimental data but with reasoned arguments (see also T 66/07, T 428/21, T 262/11, T 347/15). In T 325/13 the board even considered that there was no need for the opponent to provide further evidence because the deficiency was plausible from the cited prior art and the simple physiochemical context. All these decisions are cited in T 1076/21.

In T 100/15 an undue burden for the skilled person seeking to put the invention into practice arose from the addition of the term "controlled". It was undisputed that the contested patent did not provide a definition for controlled cooling. It had been rendered plausible by the opponent during the appeal proceedings that the skilled person did not get the required information from the contested patent as to how to perform the controlled cooling, and so it was for the patent proprietor to demonstrate otherwise.

In T 1299/15 the patent specification did not describe any embodiment for the adjustment device, and so the appellant could not prove the alleged lack of reproducibility on the basis of such an example and instead could only base its case on attacking the device's plausibility, which it then did. That shifted the burden of proving the contrary to the patent proprietor (in this case the respondent).

In the following cases, the patent proprietor was the appellant and whether the burden of proof had been shifted was an issue, but the boards in question saw no reason for such a reversal of the burden of proof; the burden still being on the opponent at the appeal stage: T 499/00, T 355/05, T 1052/13, T 1608/13, T 720/17, T 55/18.

For recent decisions citing G 2/21 (OJ 2023, A85), see T 1394/21 and T 2790/17, the latter concluding that even though experimental data had been provided in the application as filed, it was not credible on the basis of this data that the claimed therapeutic effect was achieved; post-published evidence could not be taken into account, and the burden of proof rested with the respondent (patent proprietor).