I found a Trak-Ball that is serial number 00249, so I figured it'd be interesting to see what kind of serial numbers are out there. I asked the 5200 facebook group and a bunch of people there gave me the numbers off of their Trak-Balls.
Please feel free to post your serial number and any interesting information, like Country of Manufacture and the EP codes. Or, any other code prefixes.
Here's the list.