The age of documents known long before the filing date might only be an indication of an inventive step if a need for the solution of an unsolved problem had existed for the entire period between the date of the documents and that of the invention (T 79/82 and T 295/94). Nevertheless, the long period of time to be considered was not the period that had elapsed between the publication of a document and the filing of the European patent application disclosing the teaching of that document, but that between the time the problem became apparent and the date of filing of the European patent application providing a solution (T 478/91).
A period of 23 years between the publication date of the document deemed to be the closest prior art and the priority date of the contested patent in an economically significant and frequently studied field could normally be viewed as an indication of the presence of inventive step (T 273/92). In T 203/93 and T 795/93 a period of 11 years was considered to be an indication in support of inventive step, in T 986/92 a period of 70 years, in T 478/91 80 years and in T 626/96 60 years (see also T 774/89, T 540/92, T 957/92, T 697/94, T 322/95, T 255/97, T 970/97, T 6/02, T 2271/08).
In T 330/92 the documents reflecting the general knowledge available to experts in the field of the application (injection mould technology for cashcard holders) had been published at least 17 years before the filing date of the contested patent. The board of appeal pointed out that the elements which could have led to the feature combination of claim 1 had thus long been known in the prior art. Nevertheless the experts had for all this time been "blind" to these findings. Nor had other applicants in the same field made use of the knowledge in question.
In T 1077/92 the board faced the unusual situation of a problem and its ready solution having coexisted for 100 years in general, and more recently in a field of intensive research, and still the seemingly obvious step had not been taken. The board concluded that, as no other explanation could be found, this must have been because inventive insight was needed (T 617/91).
In T 123/97 the failure to adopt an obvious solution to the technical problem underlying the patent in suit may have resulted from a variety of causes; for example, there may have been a commercial reason for not adopting this new technique, because the old technique was found satisfactory by the clients and could also be improved, thus avoiding considerable investment costs involved in the adoption of a new technique on an industrial scale.