Quoted from Isochronic_Frost:

The number is usually random because they skipped large gaps purposefully so rival manufacturers couldn’t figure out how large production runs are, similar to how new Stern’s don’t really give you an idea of how many are made. It’s bad for business to know how many games exist unless that’s a selling point. (I.E. Spooky Boutique games or Limited Editions)
I would recommend looking at the IPSND.net where users submit serial numbers and they use an algorithm to try and determine the scope of the serial number range. It’s a lot of guesswork. The more numbers submitted the better idea we have of them production run and where the gaps were.

Quoted from jrpinball:

Rest In Pieces.