According to Art. 123(2) EPC the European patent application or the European patent may not be amended in such a way that it contains subject-matter which extends beyond the content of the application as filed. The revision of the EPC has introduced a purely editorial change to the wording of Art. 123(2) EPC to bring it into line with Art. 123(1) EPC. However, Art. 123(2) EPC 1973 and Art. 123(2) EPC are substantively the same.
"The underlying idea of Art. 123(2) EPC is that an applicant is not allowed to improve his position by adding subject-matter not disclosed in the application as filed, which would give him an unwarranted advantage and could be damaging to the legal security of third parties relying on the content of the original application (see G 1/93). An amendment should be regarded as introducing subject-matter which extends beyond the content of the application as filed, and therefore unallowable, if the overall change in the content of the application (whether by way of addition, alteration or excision) results in the skilled person being presented with information which is not directly and unambiguously derivable from that previously presented by the application, even when account is taken of matter which is implicit to a person skilled in the art." (Guidelines H-IV, 2.2 - June 2012 version).
In G 2/10 (OJ 2012, 376) the Enlarged Board confirmed that the generally accepted standard for assessing any amendment for its compliance with Art. 123(2) EPC is the test established in G 3/89 and G 11/91. Thus, amendments are permitted within the limits of what the skilled person would derive directly and unambiguously, using common general knowledge from the application as filed ("gold standard", the wording and the importance of which are recalled in T 248/12).
In G 2/10 (point 4.5 of the Reasons) the Enlarged Board also stated that "the test … must be that after the amendment the skilled person may not be presented with new technical information."
It further must be taken into account, as indicated in the decision T 383/88 of 1 December 1992 (point 2.2.2 of the Reasons), that the slightest doubt as to the derivability of the amendment from the unamended document would rule out the amendment.