I don't have specific knowledge of that car, but something similar occurred for the 2004 convention. I don't know if it's standard for each year or not.
For 2004, one of the normal convention cars available for members to purchase was a TCA 50th anniversary Mint Car. At the banquet, there was a special version of this car (similar to your story, one per table, so on the order of less than 100 made is not unreasonable) that was a table prize. For the 2004 car, it had specific lettering on one of the windows (actually had the words "Banquet Car", I believe)differentiating it from the normal convention car.
So it would seem very plausible that there are 2 versions of the car you are describing. Unfortunately I can't help with figuring out what the special markings might be for that one if this is the case.
-Dave