Just saw this old 500 on eBay. Originally from 1955 but has several stamps on it. It got me thinking, how many stamps have you found on a phone?
https://www.ebay.com/itm/254015194100
Every time it's "refinished" it gets a stamp.
I've had a few like that myself.
I have seen phones less than 7 years between original date and last date with up to 4 date stamps on the base including with original. these were pre -1960 on all dates. I think at that point in time they tested the telephone when returned from service. I think the phones with lots of dates were from high turn-over installations.
I think the the stamp at that time was more of a "tested and meets current standards" sign off, meaning tested and upgraded if needed.
On phones where the stamps have a 5+ year difference, I think those date stamps are rebuilds .
My comments on this topic are opinion/observation based. and are rule -of-thumb type statements.
Jim S.
I think you're right Jim about the '50s. I've seen stamps like "S1257", which I've taken to be a service in December 1957 between installs. I had a '58 500 with a similar marking in '59. In that case the phone was mostly original but the dial had been replaced with a 95B blank and the shell was mis-matched also. These often don't have other refurb-center marks on the base.
Refurbs, on the other hand, often have lots of black brushed-on paint with the model number and/or date painted over, changed feet, and lots of replaced parts (have to say I just don't like those much..... 😉)
I think the forum had an informal contest once to see who could find a 500 base with the most refurb stamps.....