In the old days you could indeed just walk in. When I got mine, the guy was sat across the other side of the office typing it up, he shouted across "what licence do you have....what ratings do you have"...he never checked my JAA licence. However as the FAA one is invalid without the JAA one, then it would have done me no good to add a few
. Indeed I went in with my mate when he was getting his issued, and at the time, his licence was with the CAA in Gatwick, 5000 miles away. He still got the FAA airmans certificate issued, but of course couldn't use it at the time.
You can check some details about yourself on the FAA webiste, for example ratings. It won't give you any certificate numbers or anything though. I believe your FAA cert number is made up of your foreign licence number....I think.....I haven't got my licence here to check but it sort of rings a bell......
good luck with your crusade,
EA