When I joined AMA on Jan 1, 1963, I was given the number I currently use, a 4-digit. About 1985 I let my membership lapse, so when I re-joined again in 1995, they gave me a 6 or 7 digit number. I then requested the return of my old number and got it.
The 4 digit number had nothing to do with being a CD, but I did get my CD license sometime in the '70's. As I recall, I just had to get a couple of CD's or Leader members to sign off on my dubious character. A few decades later, to re-activate my CD'ness, I had to take a friggin' test and answer a bunch of questions about R/C crap that didn't matter at all to me...but it was an "open book test"...and I still couldn't find one of the answers about some R/C crap. Leading me to realize that the AMA rulebook as a whole was a horribly disorganized pile. Still is, IMO.
AMA recently (last 5 years or so) pretty much demanded that CD reports and Sanction applications be done online, at which point I refused to do it anymore.
I am curious why Joe's wife joined AMA just to launch his Navy Carrier models. Does not compute!
FYI, NEVER allow anybody to be an "ED" without being a current AMA member. Even as secondary insurance, it's (barely) better than relying solely on your homeowner's or renter's insurance.

Steve