The discretionary power pursuant to Art. 114(2) EPC applies to facts and evidence filed late (see e.g. T 502/98, T 986/08, T 66/14). What is meant by "in due time" for the purposes of Art. 114(2) EPC requires interpretation.
The parties in inter partes cases are subject to a particular duty to facilitate due and swift conduct of the proceedings, in particular by submitting all relevant facts, evidence, arguments and requests as early and completely as possible. This duty is reflected in the EPC provisions governing the handling of late submissions: Art. 114(2) EPC as a general provision; R. 137 EPC for the grant procedure; and R. 76(2)(c) and R. 80 EPC for the opposition procedure; R. 116(1) EPC concerning the final date for making written submissions in preparation for oral proceedings (for appeal proceedings, see the Rules of Procedure of the Boards of Appeal; see chapter V.A.1.2. below).
The boards have stressed that opponents are required to submit all their objections during the opposition period, setting each out in full (T 117/86, OJ 1989, 401). Under R. 76(2)(c) EPC, the notice of opposition must contain a statement of the extent to which the European patent is opposed and of the grounds on which the opposition is based, as well as an indication of the facts and evidence presented in support of these grounds.
Notwithstanding the above, according to the case law of the boards of appeal, not only the facts and the evidence submitted by the opponent within the nine-month period to file an opposition and those possibly submitted by the patent proprietor within the four months given for replying to the grounds of oppositions are "filed in due time". The filing of facts and evidence within subsequent periods of time may also be in "due time" when it occurs in accordance with the principle of procedural economy and, therefore, when the filing party has observed a fair degree of procedural vigilance (T 502/98 referring to T 201/92, T 238/92, T 532/95 and T 389/95; see also e.g. T 574/02).
Accordingly, new facts, documents and/or evidence are regarded as having been filed on time if their filing was occasioned by an argument or a point raised by another party so that, under the circumstances of the case, they could not have been filed earlier. According to T 502/98 this may occur, for instance, when certain facts or evidence became relevant only after a party has submitted an unforeseeable amendment of the claims or a new experimental test report or has challenged for the first time the existence of common general knowledge. In such cases, a diligent party normally has no obligation to retrieve and file such facts and evidence before such action of the other party (cited e.g. in T 986/08). See also T 623/93, where the board held that, where amended claims were introduced in the opposition proceedings there could be no objection to the opponent's submitting new citations and new arguments against the new claims (with reference to G 9/91, OJ 1993, 408, point 19 of the Reasons).
Therefore, the filing of new facts and evidence in direct response to new submissions by the other party (T 389/95, T 320/08, T 1698/08, T 1949/09), or at the earliest time possible in the proceedings (T 468/99, T 2551/16), or promptly after their relevance has become apparent (T 201/92, T 502/98, T 568/02, T 574/02, T 986/08), has been considered to be "in due time" (see also T 156/84, OJ 1988, 372, but also e.g. T 1734/08 and T 733/11, which considered submissions filed outside the period specified by Art. 99(1) EPC to be late-filed, without considering the observance of procedural vigilance).
In T 117/02 the board stated that in the case of a request to introduce late-filed submissions (here: a new ground of opposition and new arguments and evidence) the right to be heard should be granted before those late-filed submissions were rejected. In summary, an opponent must be given an opportunity to respond in an appropriate way when the subject of the proceedings has changed, for example due to amendment. Depending on the nature of the amendment this may involve the filing of further documents (T 366/11).
In T 2165/10, the board shared the respondent's view that the appellant (opponent) should have included an indication of the alleged public prior use submitted later in its notice of opposition and indicated/filed all evidence in its possession at that time. It did not accept the appellant's argument that the documents in its possession at the time of filing the opposition were considered by the appellant not to be enough to constitute a complete chain of evidence.
In T 628/14 the board recalled that, according to the established case law, R. 116(1) EPC should not be construed as an invitation to file new evidence or other material departing from the legal and factual framework of issues and grounds pleaded as established with the notice of opposition. Also, the fact that the opposition division expressed a preliminary opinion in its communication did not necessarily justify the filing of new evidence, unless this was in reaction to new aspects raised in the communication.
The board in T 66/14 observed that, according to case law, evidence first submitted by an opponent after expiry of the nine-month period under Art. 99(1) EPC was generally to be regarded as late for the purposes of Art. 114(2) EPC, and that R. 116(1), fourth sentence, EPC was not to be understood to mean that a fresh period during which new evidence could be filed without being treated as late was triggered on issue of the summons to oral proceedings (T 841/08). However, there may be cases in which special circumstances justify an opponent's not filing evidence until after the nine-month period under Art. 99(1) EPC and in which, therefore, that evidence is not to be treated as late for the purposes of Art. 114(2) EPC (T 532/95). In particular, new evidence submitted after the date referred to in R. 116(1) EPC is to be admitted if the subject of the proceedings has changed.