I think posters are reading this the wrong way round - the original question is can you operate an aircraft with an MCTOM that is greater than the 't' value, if you are actually at an AUM below that 't' value?
Logic says of course, but it probably depends on exactly what the 't' value means. Is it the maximum mass of an (any) aircraft the deck is designed to accept, or the MCTOM of the specific aircraft for which the maximum 'D' value used is? CAP437 isn't very specific.