There is no strict rule that a decision has to deal with all the points which are or may become contentious between the deciding authority and the parties concerned. For reasons of economy it is, however, appropriate to base a rejection on a number of separate reasons, in order to come as early as possible to a final decision in a case. Therefore an Examining or Opposition Division should deal with those questions which may be expected to become relevant at second instance insofar as this is possible without substantial additional effort, so that, in the event of a successful appeal, the matter does not have to be remitted to the deciding authority by the Board of Appeal.
An example would be where an application has been refused because a particular claim lacks novelty, but the decision argues that the claim also lacks inventive step. It is essential in such cases that the applicant should have been given an opportunity to comment on all grounds on which the decision is based.
It is in fact possible to cite further grounds on which the decision is not based, provided these appear not in the actual decision but only after the grounds under a separate heading such as "Additional comments". It is then clear that they are not actually part of the reasons for refusing the application.