In T 329/99 the board stated that a clear distinction had to be made between the questions whether a particular embodiment was disclosed by an application, be it explicitly or implicitly, or/and whether that embodiment was merely rendered obvious by the application's disclosure (referring to T 823/96; see also T 1171/08). A particular technical embodiment might be rendered obvious on the basis of the content of an application as filed without, however, belonging to its explicit or implicit disclosure and therefore without serving as a valid basis for amendments complying with the requirements of Art. 123(2) EPC 1973.
In T 598/12 the board had to assess whether the skilled person using his common general knowledge would regard the additional technical information encompassed by the claims after the amendment as directly and unambiguously implicitly disclosed in the parent application as filed. The board stressed that it was not to be investigated whether this technical information derived from the prior art knowledge in the field. What had to be assessed was whether the notional skilled person working in the field would consider something as directly and unambiguously disclosed in the light of this common general knowledge. It recalled that the assessment of what information was implicitly disclosed in an application could not go beyond the limits of what the skilled person would objectively understand to be a direct and unambiguous consequence of the explicit disclosure in the particular case. Moreover, when performing this assessment, the common general knowledge could not serve to enlarge or replace, in a subjective or artificial manner, the actual content of the specification. The investigation of the actual disclosure in a patent application as filed could not turn into an investigation of obviousness or a search for obvious alternatives of the actual disclosure in the light of general prior art documents.
Referring to T 598/12, the board in T 2489/13 confirmed that the criterion of whether alternatives are well known in the field could not be taken as a valid approach for the investigation of at least an implicit disclosure of what is directly and unambiguously derivable from an application as filed within the meaning of Art. 123(2) EPC.