Quoted from UKCatsFan76:Looks like a run of 300 and a run of 510, so around 810 from reading playfield labels.
Serial numbers that I have seen also support over 600, so 800 sounds about right.
I think it was just one batch of 510 playfields that were mislabeled originally as a batch of 300. I have yet to see a playfield from the 510 batch under 337.
This picture is from the IMVE thread.
(#318 of 300)
Looks to me like they just changed the total number to 510* at some point and added the * like it was some kind of correction.