In T 447/00 and T 448/00 the board was not convinced that the approach taken by the department of first instance, that the admitted existence of four mistakes in respect of the same procedural act could not, by definition, be qualified as "isolated", took sufficient account of the issues to be considered in connection with Art. 122(1) EPC 1973. The board stated that the case law of the boards of appeal referring to an "isolated mistake within a normally satisfactory system" did not normally require that only a "single" error had occurred in relation to a case for which re-establishment of rights was sought. It was not excluded that, in certain circumstances, a chain of errors could well be qualified as "isolated".

In T 808/03 of 12 February 2004 date: 2004-02-12 the board held that the condition of "an isolated mistake by a usually reliable person" was not met in the present case, as the responsible person had made a second mistake when processing the reminder of a system for monitoring time limits. See also T 1149/11, T 1325/15.

In T 1325/15 the appellant argued that since a system with a cross-check would identify any single mistake, the term "an isolated mistake" had to be understood as encompassing more than one mistake. In the case in hand, the failure to file the notice of appeal in time had been caused by a combination of isolated mistakes and the appellant argued the requirement of all due care was therefore complied with. The board rejected the appellant's proposition; having a satisfactory system in place does not relieve a representative of his duty to take all due care required by the circumstances when performing procedural steps forming part of that system.

In T 1815/15 the first employee (an attorney's clerk) made a mistake by mentioning the wrong paragraph of R. 82 EPC in the heading of the accompanying letter to the EPO, overlooking the surcharge required by R. 82(3) EPC. It appeared to the board that the firm of attorneys representing the patent proprietor was equipped with a monitoring system which would normally detect this kind of mistake. Therefore the mistake by the second employee when comparing the communication from the EPO with the actions performed by the first employee may be ascribed to an isolated error of the second employee, which the board ascribed to a personal and isolated error in a system which normally should prevent such deficiency.