As far as the assessment of late filing in opposition proceedings is concerned, the rulings of the Enlarged Board of Appeal in G 9/91 and G 10/91 apply. According to these decisions, in principle, the opposition is to be examined to the extent and on the grounds submitted during the period for opposition. Under Art. 114(1) the opposition division may go beyond this framework if prima facie maintenance of the patent is prejudiced. The principles developed by the Enlarged Board with respect to new grounds also apply to late-filed facts and evidence (see T 1002/92). Therefore late-filed facts and evidence are to be admitted into the proceedings only if they are prima facie relevant, i.e. if they would change the envisaged decision, see E‑VI, 2.
If a patent proprietor replies to a notice of opposition by amending the patent, such a request for amendment cannot be considered as late-filed and has to be admitted into the proceedings (Rule 79(1)).
Thus, if the proprietor limits the patent to the subject-matter of a dependent claim as granted, new facts and evidence submitted by the opponent in reply to this amendment are as a general rule to be treated as late-filed and only to be admitted under Art. 114(1) if they are prima facie relevant because the opponent must be prepared for this type of amendment and must have provided material during the nine-month opposition period.
If the new facts and submissions are not prima facie relevant, they are to be disregarded under Art. 114(2). An exception to this rule is where the patent specification as granted contained a large number of dependent claims and the opponent could not reasonably have been expected to deal with all of them in the notice of opposition.
If, however, the proprietor amends the patent at an early stage of the proceedings in a manner not foreseeable by the opponent, e.g. by taking up features disclosed in the description, the opponent will have the opportunity to provide new facts and evidence, i.e. possibly even to submit a new ground for opposition and new documents. Such a submission has to be admitted into the proceedings because the subject of the proceedings has changed. At a late stage in the proceedings such unforeseeable amendments are subject to the criterion of "clear allowability" (see H‑II, 2.7.1).