I also go by my middle name socially. All of my "official" records (military ID, driver’s license, ssn, etc) all have my first name and, mostly, middle initial. All of my c-cards have my social name "Dale Hall." I don’t go by my first name in any unofficial instance and since I dive for fun, "Dale" will always be on my c-cards. And, to answer one of the OP’s initial question, I have never had anywhere in the Caribbean check my passport or any other official ID against my c-card when diving. 99% of the time, the stuff is in the hotel room or onboard the cruise ship when I’m diving anyway.