You were indeed correct. No BC on the bell, but a run-of-the-mill Evette-Schaeffer from the late 60's. The repair tech is new and read the serial number from the wrong book as you projected.That is a late 60's-1970's Evette-Schaeffer, made by Santoni, Italy. If it has a lily insignia on the bellbrace.
The person (whether you or someone else) looked at the Santoni/Evette serial number and cross-referenced it to the Buffet (France) serial number lists....thus came up with incorrect fabrication date.
They were ubiquitous band horns/student horns in Europe in their day. Not bad players at all, once worked up into good shape. But even one in good, serviced playing shape has only a market value of maybe $300-350 tops.
In non-playing shape, as a project horn, worth perhaps $125.
If perchance the bellbrace insignia reads "BC"...they you likely have a stenciled Buffet Dynaction or Super Dynaction, which IS a FIND. But I doubt it is one of those.
Looked like a solid horn for being stuck in an attic for 20+ years... but the guy paid $600 for it and it needed somewhere in that ballpark for a total repair job too. All in all, he just came and picked it up and went on his way.