In T 11/82 (OJ 1983, 479) the board stated that the addition of a discussion of the advantages of the invention with reference to the prior art did not necessarily constitute a contravention of Art. 123(2) EPC 1973. Whether Art. 123(2) EPC was infringed depended on the actual language used and on the circumstances of the individual case. See also T 725/05 where the addition of an analysis and discussion of a prior art document which went far beyond the dislcosure of said document was considered contrary to Art. 123(2) EPC).
In T 37/82 (OJ 1984, 71), for example, a technical feature was clearly disclosed in the original application but its effect was not mentioned or not mentioned fully. It could however be deduced from the original application on the basis of normal expert considerations. T 434/97 stated that when introducing features not explicitly disclosed, it was necessary that such features could be unmistakably and fully derived from the original text (in this case the parent application); this corresponded to the opinion in T 37/82. In the case at issue the added effect could not be derived from the original text.