Ah, here's the answer to why I had not noticed the 3+2 before: I had only been looking at Kiloton 5s and JB-5s (which are still 4+1) and not the L/M-2500s (which are 3+2)
I am probably putting more than you care to know here, but in case anyone later finds this and is hoping to reference it...
L2500 is currently 3+2 and has been for a long time. Early L2500s and the L5500 were 4+1 (a bulkier version of 4+1 that does not look like the current 4+1). The non-sickle headstock L5000 was a 4+1 that looks closer to the current 4+1. Sickle stock L5000 was also 4+1, but had its own non-G&L looking shape going on.