Linguistic errors, errors of transcription and other mistakes in any document filed with the EPO may be corrected at any time, as long as proceedings are pending before the EPO. However, where the mistake is in the description, claims or drawings, both the error and the correction must be such that it is immediately evident (at least once attention is directed to the matter):
Regarding (i), the incorrect information must be objectively recognisable for a skilled person, using common general knowledge, from the originally-filed application documents (description, claims and drawings) taken by themselves.
Regarding (ii), the correction should be within the limits of what a skilled person would derive directly and unambiguously, using common general knowledge, and seen objectively and relative to the date of filing, from the originally-filed application documents.
Evidence of what was common general knowledge on the date of filing may be furnished in any suitable form.
Correction under Rule 139, second sentence, is of a strictly declaratory nature and establishes what a skilled person, using common general knowledge, would already derive on the date of filing from the parts of a European patent application, seen as a whole, relating to the disclosure (see G 3/89 and G 11/91 mentioned above). Therefore, the complete replacement of the application documents (i.e. description, claims and drawings) by other documents is not possible (see G 2/95).
However, during examination proceedings it is to be noted that such requests for correction can be considered only until such time as the decision to grant has been handed over to the EPO's internal postal service, for transmittal to the applicant (in written proceedings), or has been pronounced in oral proceedings (see G 12/91).