And he looks like Santa (well, he did when he had that big white beard).
Perhaps he thought mentioning memnbership in OTO was enough and didnt feel the need to add his high position as a reference. I know authors are not encourage within the OTO to list their role in the organisation in order to sell books outside the order or give some type of validity to the work. They would prefer the works to stand on their own merits. LMdQ is a bit different though, he is very 'out there' touring, giving classes, etc.
In any case, membership in OTO might not be that good a reference, any person can study general Hermetics, Tantra, Tarot etc, and come to whatever level of knowledge, understanding and wisdom that they will. The only REAL OTO specific gnosis is the OTO initiation rituals (which is not up for public discussion) and the Gnostic Mass Ritual / ceremony (which most find too boring to be up for public discussion).
Being a member of OTO does not necassarily mean that a book you write will be good ... or accurate.