Jimmie D,
Your understandings seem reasonable, with a few clarifications.
At least through 1950, the front and rear chrome bumpers were standard in 1/2 ton trucks. It looks like from 1951 and later Advance-Design trucks, a rear bumper was optional.
1952 and 1953 bumpers (standard front bumper and optional rear bumper) were not available in chrome. In 1954/55 a painted front bumper was standard (optional chrome front bumper was now available); and, in 1954/55 painted or chrome rear bumpers were options.
Yes, parts that supposedly changed for a specific year did not change on a specific date. They changed when the older part in that factory ran out.
