LeftyBassist.com

I simply do not know.

What is the true deal on strap button felts? Were they present on vintage basses or no? Lately I've seen them both ways.

yes, I'm referring to the little felt donut between the body and the underside of the strap button...

sometimes they're white, sometimes black and sometimes missing and always "period correct"....

They are on my '74 Jazz which is all original. Other than that I don't know their usage.

I always figured they were there to just prevent wearing off the finish

Yep they can keep the finish from cracking

I've been repairing guitars and basses since 1969. ALL the instruments I began working on were original, now expensive collectable ones. I NEVER, ever saw felt washers used on any Fender guitar or bass, until the introduction of the Mexican made instruments. That '74 J-bass may have had the buttons changed- or someone simply installed the washers themselves- it's very easy for even a mechanical novice to do it. I bought a brand new lefty Fender P-bass, maple neck, black, lefty case- at Sam Ash in Manhattan, in 1973. It did not have felts. Did have the weatherstripping mute under the bridge cover, though.
I went to work as a guitar repairman for Sam Ash in Brooklyn, in 1979. Worked there 3 years. From my experience there seeing literally hundreds of Fenders, the felts were not installed from the factory on any of the instruments I saw.
In my opinion, those felt washers make the instruments look cheap.

Didn't see them at all during the 70s.

Appreciate all the responses y'all!

Recently checked over an interesting piece locally and they (the felts) were not there.

Got me curious.

It's a minor detail of no importance (I'm an expert!) but I just had to ask.

Define "interesting piece".

Was a Bluesman Vintage Tele-bass.