"during 70s 80s and 90s" - so three decades of playing, five decades of possession. Presumably he got himself a proper bass 25 years ago.
I wouldn't automatically assume that having no pics of the neck stamp but knowing that it's there is necessarily a sign of it being dodgy - after all, if he's ever had to adjust the truss rod, he'd have taken the neck off and seen the stamp, but wouldn't necessarily have thought to take a photo (or it might have been before digital cameras and cameras on phones). Still, he's going to find more demand for it if he does go the extra mile.