What should a guy make of a watch advertised as containing a Cal. 502 movement?

This doesn't seem to exist on the Omega Vintage Database nor on Naligazone. The guy who wrote up the "how to spot a fake Omega" on eBay makes reference to a 502, so that's a positive sign, right?

Is it a really rare movement?

 

http://www.ranfft.de/cgi-bin/bidfun-db.cgi?10&ranfft&2&2uswk&Omega_502

Ranfft is a pretty good movements database

 

Thank you so much for the reference! I am saving it now!
I searched OF a dozen different ways trying to find this caliber. No sooner had I given up and pressed "post" on my thread, I stumbled over the 16 page list of all calibers, in French! Lo and behold, the 502 is listed there and it does seem somewhat rare: only 14,000 created compared to the 397,000+ for the 501. So, that little heart attack averted!
Thank you again for your help!

 

It is comparable with the cal. 503. Cal. 502 is an "US export" version of the 503, as there was a higher import tax levvied on watch movements with more than 17 jewels in those days.

 

I just read an article about that...on the Constellation blog?...yesterday. Clearly I didn't absorb the key details! Thanks again for sharing that website - it's a good one and I'm glad to have access.