Has anyone seen this stamp on their neck heel ( a circle with a 1 inside of it ) and no date stamp? this is off a musicman stingray probably from the 1980's
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You might try posting this on the Guitarsbyleo.com forum - that's the G&L forum - or on G&L's "CLF Research" Facebook page.
As you may know the original Music Mans were made by CLF Research - Leo Fender's R&D company he started when he left Fender. Shortly after parting ways with Music Man Leo started G&L Guitars out of the same facility (eventually retiring the CLF Research name) so they have some insight to the Leo-era Music Mans (1976-1980). If it was made after 1980 then it could have been from any of the various subcontractors MM used until they went bankrupt (including Charvel/Jackson for a while circa 1981/82).
They have been releasing a lot of CLF Research archives that Leo left behind when he died 27 years ago on that "CLF Research" Facebook page.