MICrew843-
As I remember the 100 Ton and AB tests are almost identicle, except Masters have navigation and ABs have knots. If you recently passed the 100 ton Master exam bone up on your knots and go take the test.
STCW, Lifeboatman and RFPNW are inter-related. There are situations where none is required for service.
Basic Safety Training (BST) is only a part of the STCW requirements, but almost every company will insist that you have it.