Reasons of efficiency dictate that the search division uses its judgement to end its search when the probability of discovering further relevant prior art becomes very low in relation to the effort needed. The search may also be stopped when documents have been found clearly demonstrating lack of novelty in the entire subject-matter of the claimed invention and its elaborations in the description, apart from features which are trivial or common general knowledge in the field under examination, application of which features would not involve inventive step. The search for conflicting applications (see B‑VI, 4) is, however, always completed to the extent that these are present in the available documentation.
Source: http://www.epo.org/law-practice/legal-texts/html/guidelines/e/b_iv_2_6.htm
Date retrieved: 17 May 2021