In the past, the boards have allowed corrections under R. 88, second sentence, EPC 1973 (now R. 139 EPC) provided it was immediately evident to the skilled person that an error had occurred and how it should be corrected. In T 640/88 and T 493/90 the required correction to an error in the claim was evident from the description. In T 488/89 the reference to a parallel application enabled the skilled person to establish without difficulty the correct limit values. In T 365/88 it was ruled that an abbreviation in the claim could be corrected because it appeared correctly in the description; an additional Roman numeral I in the abbreviation of an enzyme was implicitly disclosed because at the time of filing only one enzyme of this type was known, and clarification prevented confusion with enzymes of the same type discovered at a later date.
In T 990/91 the board allowed the correction of a chemical name on the grounds that an obvious error had been made in naming a salt which was the subject-matter of the application - the molecular formula of this salt was clear from the application. However, the molecular formula corresponding to the name was different. Guided by the content of the application and taking into account cited documents which were published before the priority date of the application in question, the correction required would be immediately evident to the skilled person.
In T 417/87 the board of appeal allowed the number of a publication cited in the original description to be corrected under R. 88, second sentence, EPC 1973. In T 158/89, however, correction of a percentage range of a component was not allowed. In the board's view, the skilled person could have deduced from inconsistencies in the claims and description that an error had occurred. However, there were two plausible ways of correcting it. Since the skilled person would have regarded both alternatives as equally plausible, it was not immediately obvious that nothing else had been intended other than the proposed correction.
In T 606/90 the board allowed a correction pursuant to R. 88, second sentence, EPC 1973, in the opposition proceedings although the correction was not so obvious from the published text of the patent that it was immediately evident that nothing other than the proposed correction could have been intended. The applicant had filed typed amendments to the claims and the description and had also submitted the "working document" with the handwritten corrections for the dossier. The typed version of claim 1 omitted the detail which was now the subject of a request for correction pursuant to R. 88 EPC 1973; the same detail was present in the corresponding passage in the description. When the text was being prepared for publication of the patent, the detail in question was also omitted from the description owing to an error by the EPO. The board concluded that the omission in the description should not be taken into account when considering the admissibility of the correction. It stated that it was therefore clear that the phrase in question had been omitted from the typed version of claim 1 as a result of an error by the applicant and that the reader of the patent would immediately have noticed the need for correction of this error if a transcription error had not likewise been committed by the EPO. The correction requested was therefore admissible within the terms of R. 88 EPC 1973.
In T 955/92 the appellant had requested that under R. 88 EPC 1973 the words "silica" and "alumina" in the claims and description be replaced by "silicon" and "aluminium" respectively. It argued that the ambiguous expression "silica to alumina atomic ratio" could only have two meanings, either "silicon to aluminium atomic ratio" or "silica to alumina molar ratio" and that it was evident to a skilled person that the correction could only be as requested.
The board did not share this view. It accepted that there was obviously a mistake and that the interpretation according to the correction sought was more likely than the alternative. However, referring to G 3/89 (OJ 1993, 117), it emphasised that the correction should be unambiguously derivable by a skilled person, using common general knowledge, from the description, claims and drawings of the patent application on the date of filing. The board held that in the case in point the reasons given by the appellant to show that only the requested correction could have been intended were not based on the level of general knowledge on the date of filing. In order to arrive at the conclusion that the requested correction was the only physically meaningful one, experiments had had to be performed which needed more than common general knowledge, and the results thereof would not have been available on the date of filing.
In T 438/99 the board held that the fact that a term or phrase could not be interpreted or construed because it was unresolvably ambiguous did not necessarily mean that its deletion was a permissible amendment under Art. 123(2) EPC 1973. There remained a residual clear meaning in the ambiguous term, e.g., as in this case, that a specific direction was taught, and suppressing that fact resulted in a different technical teaching.
In T 1508/08, the board concluded that the second condition for allowability of a correction under R. 139 EPC was not met. In its view, not only did the correction fail to solve the existing problems of a lack of clarity, but it actually made things even less clear. That was one reason why the skilled person would not have contemplated the correction made by the appellant proprietor. Even if it were assumed in the appellant's favour that the skilled person would have contemplated this correction, it was not the only one possible, but rather one of at least three conceivable corrections.
The invention in case T 2230/08 concerned a method of regenerating a catalyst/absorber. The modification in claim 1 of the main request that the temperature range of 121°C to 399°C defined the regeneration temperature rather than the temperature of the incoming stream of reducing gas was, in the appellants/patent proprietors’ view, a mere correction under R. 139 EPC of claim 1 as granted. The board stated that it was not in dispute between the parties that the temperature range defined in the first step of claim 1 as granted was not disclosed in the application as originally filed. The range of 121°C to 399°C (250°F-750°F) was clearly defined in claim 1 as granted as the temperature of the incoming stream of regenerating gas. The step of providing a gas at a specific temperature was technically sensible for the skilled person. The appellants argued that the only temperature that mattered was not that of the incoming stream of regenerating gas, but the temperature at which regeneration was carried out, which was the temperature of the catalyst/absorber. The board remarked that there was no disclosure in the patent as granted that the only temperature that mattered was the reaction temperature and not that of the gas; on the contrary. The definition of the range of temperature for the incoming stream of regenerating gas in claim 1 did not appear to the skilled person as an error, even less as an obvious one. Furthermore there was no evidence that an error of transcription occurred in the case at issue; on the contrary. Consequently, the request for correction under R. 139 EPC was rejected and the range of temperature from 121°C to 399°C in claim 1 as granted had to be read by the skilled person as defining the temperature of the incoming stream of regenerating gas, but not that of the regeneration reaction. It was not disputed that claim 1 of the main request would not fulfil the requirements of Art. 123(3) EPC, should the request for correction under R. 139 EPC not be allowed.