If I am recommended from ISSB, does it mean that I will definitely be selected and be instructed to join the academy?
Generally true but not always correct. ISSB only recommends the candidates for various courses but final merit list is prepared by the concerned services only if number of recommended candidates is more than the vacancies for that particular course. In most of the cases a candidate recommended by the ISSB makes his/her way to the academy but it may not always happen. Your name may not appear in the final merit list and thus you may not be called for the training.