According to established case law of the boards of appeal, a decisive criterion for admitting late-filed documents is their prima facie relevance, see e.g. T 1002/92, OJ 1995, 605; T 212/91, T 931/06 and T 1883/12; for appeal proceedings, see chapter V.A.4.13.2.

Regarding examination as to relevance, the board explained in T 560/89 (OJ 1992, 725) that Art. 114(2) EPC 1973 allowed the EPO to disregard documents which contained no more information than the documents filed on time and did not disclose matter which could change the outcome of the decision. According to the decision in T 611/90 (OJ 1993, 50), the boards could reject late-filed evidence, documents and other submissions on the ground that they were irrelevant, i.e. no more "weighty" or "cogent" than those already on file. In T 1557/05, the appellant (opponent) filed further patent documents as prior art. The board held that late-filed evidence was admissible only if it is more relevant than the evidence already on file.

In T 1652/08, however, the board held that, in establishing whether a document was prima facie relevant, the decisive factor was not whether it was even more relevant than a previously filed document, but rather whether it was prima facie relevant for the outcome of the case.

In T 2165/10, documents E1-E10, which related to an alleged public prior use, had not been admitted into the proceedings by the opposition division. The board held that the prima facie relevance test had been exercised correctly. The opposition division had considered, with regard to novelty, that E1-E10 did not disclose a number of the claimed features and, with regard to inventive step, that they did not deal with the problem underlying the contested patent. Since there was a document (D4) that related to this problem, the board could not find fault in the division's reasoning that the prior use was less relevant as the starting point.

Prima facie relevance is ascertained on the face of the facts, i.e. with little investigative effort, which reflects the need for procedural expediency in considering and admitting late-filed facts and evidence (T 1883/12). The interest in procedural expediency was also expressed in the approach of T 1557/05 not to admit late documents which, prima facie, are no more relevant than what is already on file. In this regard the board added in T 1883/12 that relevance is decided in relation to facts to be proven, and if late documents (here: patent documents), on the face of it, are not more relevant to those facts than admitted evidence and thus appear to add nothing, it is perfectly reasonable in the interest of procedural economy not to admit them.

Citing T 1652/08, the board in T 66/14 confirmed that, when it came to examining a late-filed document's relevance, the decisive factor was not whether it was even more relevant than one previously filed but whether it was prima facie relevant for the outcome of the case. That could not be assessed in isolation from the submissions put forward by the party submitting it; in exercising its discretion, the opposition division had to consider what objection the late-filed document was supposed to substantiate.

In T 1485/08, the opposition division had decided not to admit the late filing (on the day of the oral proceedings) of an English translation of a Korean patent which had been filed with the grounds of opposition. The board noted that the document (Korean patent) had been filed with the notice of opposition against novelty of the patent in suit. Although not in one of the official languages of the EPO, from the use of various English terms in the description of the document it was already discernible that its subject-matter was related to the claimed subject-matter. The board was of the opinion that the opposition division in not admitting the English translation for the sole reason that it was late-filed, without having examined its relevance or considered any other criteria, did not properly exercise its discretion.

For examples of cases where the boards were satisfied that the opposition division had considered the correct criterion, prima facie relevance, and had done so in detail and in a reasoned manner, see e.g. T 1643/11,T 782/13, T 2513/11 and T 572/14.