great addition to the topic!
WAG
I'd bet that based on volume, some/all of these "Y" coded "
PREFERED CUSTOMER" accounts received semi-personalized (single alpha character prefix'd VONs) Order Forms direct from Chrysler for specifying their fleet vehicles.
I believe "S" & "Y76" reference the "General Equipment Leasing Corporation (Gelco)", although I couldn't find much on the 'net about the business in the early '70s I think this is a reference to it:
http://en.wikipedia.org/wiki/Gelco& due to the nature of fleet/lease/rental vehicles these usually average (non-collectable status) vehicles, did not survive the '70s - and we see very few of them today.
..... fast forward to 1972 - "Y24" - C.L.C. Direct Leasing
C.L.C. - does anyone know a source for the actual translation?
Chrysler Lease Car? Chrysler Lease Corporation? other??
here's an official "Chrysler Leasing System" logo from 1969