I've recently acquired several Bell-matics and my curiosity has again gotten the better of me. In an effort to sort parts mash-ups from original configurations, I have started to collect case back and dial data.
Having done this for the last year with the World Timers, I will say the Bell-matics are much more common. I have gathered over 400 watches with almost no effort (aside from the collecting part) - no searching sales threads from 10 years ago, or the darkest corners of google.co.jp.
With just the basic model and serial numbers cataloged, I am seeing some interesting trends that I thought I would share.
The model numbers appear to have been released in order, so 7000's date back earlier than 7010's, the 6000's were released before the 6010's, then the 6020's and so on.
It would appear that models ending in 1 and 2 are successive, replacing the prior - for instance the 4006-7000 seems to have been replaced by the 4006-7001 and then the 4006-7002 - so I don't think those are regional variants. This trend follows on all other models in the 4006 family
Models ending in 4 or 6 appear to be SGP - so the successive thing seems to be for the 0's to 1's to 2's - stopping there.
Models ending in 9 are the US Market versions
I've started a page that collates the data as I collect it here: