Respectfully, I don't find this very plausible. The exit/entry of a cruise ship when it's docked at a visiting port is a small and tightly controlled, single-file bottleneck. There is even an x-ray detector for your bags when you re-enter the ship. It isn't like the self-checkout line at the grocery, and there would be no way to scan two different ID cards on the way onto or off the ship. It would be about the same thing as trying to scan someone else's boarding pass at an airplane gate to 'prove' they got on the plane.
I'm also not sure what the point would be of "sneaking" off at Bimini--the Bimini islands are tiny, so he would be spotted pretty quickly. They're also very, very close to the coast of Florida, so if he wanted to escape from the US for some reason, he could just do that ... from Florida.
Finally, I don't think anyone's turned up any reason he would want to escape from the United States.
<modsnip - no link>
I understand what you are saying. We all have different theories on this because none of it makes any sense.
I have been on quite a few cruises and I visited Bimini on one of them. There is normally a bit of chaos getting back on the ship because a lot of people do not have their sign and sail card out (or they can't find it) and those people step to the side so that others can continue to move through the line. Also, when putting bags on the belt for the xray machine a lot of people also fumble around to get all the stuff out of their pockets etc and cause delays in others boarding etc. You are correct, it does turn into a bottleneck at times. I have seen one person hand 4 or 5 sign and sail cards to the person scanning them in and say I have all of their cards and kind of randomly point to the people around them. While the crew certainly seem to do their best to verify all of the peoples cards they are handed (or that one person is standing their handing to them one by one) I think it could happen.
My theory is that he never got back on the ship in Bimini and had help from another family member or friend and something like this happened. I do not have a theory on why he would want to disappear, just that I think he wanted to disappear. Bimini has a ferry service that runs 3 days a week to and from Ft Lauderdale and another one that runs to Freeport Bahamas. Also, many personal boaters travel to and from Bimini from the US and other Bahamian islands daily because it is a short trip and the beaches on Bimini really are nice. We actually saw a boat from Miami that was doing PR for something when we were in Bimini and they pulled up just outside of the swimming area, blasted music and welcomed anyone to come on board that wanted to check the boat out. (It was a beautiful smaller yacht.)
Continuing with the theory that he wanted to disappear, he could have easily traveled to Bimini prior to this trip and made arrangements with one of these boaters to get a "ride" off Bimini, stash some starter money etc. It all sounds wild I know, but crazier things have happened.
Also, there are two videos of him dancing in the atrium of the ship on Saturday night, the night before the ship docked in Bimini, and some family photos that have been released from Saturday night, but there have been zero, (at least that I have been able to find) videos or photos of him onboard the ship after the group got back on in Bimini. There have been zero people from the group that I have found that have stated publicly to media sources or on social media as to what he did once he got back on the ship. There has been no timeline. (i.e. did he go to dinner with the family that night? A Show? The casino? Etc.) If this info was put out publicly it could certainly help other passengers that were on that cruise possibly remember seeing him somewhere that evening prior to his brother seeing him or hearing him at 2AM. Also, no other passengers from that sailing have come forward to the media (news or social) to say they remember seeing him at X place on the ship or have come up with photos or videos showing him in the background somewhere. People always have their phones out these days onboard to record everything... I feel like if he was on that ship, someone would be able to show him on that ship.
Also, Even though his father stated to the media that his mother had his ID and birth certificate, he could very well still have his military passport from his service in the Army (not sure if they get to keep their passports once they leave the service; my stepson who is in the Army is going to try to find that out for me) or gotten a civilian passport without the knowledge of his family.
I am sure LE is researching all these ideas already (along with all of the other possibilities) and hopefully that is why they have not made any more public statements to the press yet.
Whatever happened to him or wherever he is, I hope that he is found safe and if he is trying to just disappear for a while, I hope that he finds a way to contact someone from his family to let them know he is ok and just taking some time.