It's a tricky business no doubt because confirmation bias is a thing.
However, I was once asked to solder a friend's Celestion 44 cable connectors where they met the drive units inside the cabinet.
The existing tag connectors looked pitted and dull and after hardwiring the cables (after stripping and cleaning) the sound noticeably changed.
The tonal signature was still the same, but the pace and dynamics seemed to have been given a shot in the arm.
Even 6 months later, when listening to the the Beach Boys Sunflower double CD I could not escape the impression.
Thankfully, my friend Mitch was pleased with the results but I daresay there might be some who would prefer the previous more laidback nature of the speakers.
Just how they sounded when new, early 1970s would have been anyone's guess.
Anyway, I'd like to think all decent loudspeakers nowadays are either hardwired or use non tarnishing tags inside.