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Preliminary opinion issued in T 116/18

Following the Enlarged Board of Appeal decision G 2/21 (“plausibility”) earlier this year, the referring Board has issued its preliminary opinion on how to take EPO appeal no. T 116/18 forwards. It is clear the Board is uncertain how G 2/21 is to be applied, noting several interpretations of that decision seem feasible. Thus, new case law appears to be needed to help those using the European patent system understand the circumstances under which post-filed data can be relied upon by a patent proprietor in the assessment of inventive step.


In the opposition proceedings giving rise to EPO appeal no. T 116/18, the proprietor of European patent no. 2484209 filed experimental data dated after the filing date of the patent allegedly showing that two insecticide compounds had a synergistic effect when used in combination with each other. During subsequent appeal proceedings, the Board held it was decisive for the assessment of inventive step whether the post-filed data could be taken into account.

Accordingly, the Board turned to case law to help it decide whether to consider the proprietor’s post-filed data, but concluded divergences in the case law meant no clear path forward could be determined. Specifically, and as explained in more detail in our article of February 2022, the Board held that three distinct lines of case law exist, each applying different tests for deciding whether post-filed data can be relied upon by a patent proprietor in a particular case.

The Board therefore referred to the EPO’s Enlarged Board of Appeal as G 2/21 the question of whether (and if so, when) post-filed data can be relied upon by a patent proprietor in support of inventive step. In its decision, the Enlarged Board held that post-filed data can be taken into account when assessing inventive step, provided “the skilled person, having the common general knowledge in mind, and based on the application as originally filed, would derive said effect as being encompassed by the technical teaching and embodied by the same originally disclosed invention”.

Following the issuance of that decision, Board 3.3.02 has recently issued its preliminary opinion in the case underpinning the referral. This is an important step in understanding how decision G 2/21 will be applied by the EPO moving forwards, providing an insight into when post-filed data can be relied upon in future cases.

Interpreting G 2/21

Interestingly, the Board in T 116/18 appears unsure how to apply G 2/21, apparently believing there are two ways the Enlarged Board’s conclusions can be interpreted.

Firstly, the Board suggests that G 2/21 could be understood as meaning that post-filed data can be taken into account as long as the technical effect the data are alleged to support was plausible / not implausible based on the application as filed, having regard to the skilled person’s common general knowledge. In other words, and as stated by the Board in its preliminary opinion, G 2/21 can be interpreted as reformulating the tests used in the ab initio plausibility and ab initio implausibility lines of case law into a single test that would have resulted in the same decisions being reached had it been applied in each of the cases giving rise to those two lines of case law.

Alternatively, the Board indicates that G 2/21 may mean that post-filed data can be taken into account only if the technical effect is derivable from the application as filed, and thus that effect does not change the nature of the invention as originally disclosed. As noted in the Board’s preliminary opinion, such an interpretation would sweep aside the concept of “plausibility” and would mean that plausibility case law should no longer be applied; instead, the application as filed would need to indicate in some way that the technical effect the post-filed data allegedly supports is achieved by the claimed invention. This is the interpretation given by my colleague, George Schlich, in his article of March 2023.

The Board has also noted that the parties may have other interpretations of their own.

It seems clear from the preliminary opinion that Board 3.3.02 is unwilling to commit to a particular interpretation of G 2/21 at this time. As such, the Board has invited the parties to provide their views on how G 2/21 should be interpreted at the oral proceedings for appeal no. T 116/18, which are due to be held in July this year.


For those hoping G 2/21 would provide certainty as to whether (and if so, when) post-filed data can be taken into account in the assessment of inventive step, the comments of Board 3.3.02 will be somewhat disappointing. The question of whether a technical effect must be plausible, not implausible, or somehow derivable from the application as filed in order for post-filed data to be relied upon in support of an inventive step remains unanswered, and further decisions of the EPO’s Boards of Appeal are needed to clarify this.

If you have a case where post-filed data is at issue, then Schlich would be happy to advise you further on the interpretation and application of G 2/21 to help you take your case forwards.

Our articles are for general information only. They should not be considered specific legal advice, which is available upon request. All information in our articles is considered to be accurate at the date of publishing.


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