The point is proper phraseology should be used at the appropriate times and therefore many airlines tend to standardise it in order to avoid any possible confusion from flight crew should the need arise. Your OM(A) Chap. 8 might have some guidelines for situations warranting the declaration of a mayday or a pan call, and that is basically how your operator wants you to deal with that particular problem. I have seen operators where, on a twin, the inability of an engine to deliver up to full unrated go around thrust was considered an engine failure and warranting a mayday call (even with an engine running just a bit less than normal cruise thrust and the other normal) or running on a single engine driven gen, and other airlines where a V1 cut with no fire is a pan call and so on. It is not always black and white.