Another tangent....
How about an artist that uses different band members from one album to another? Or one that uses a different band in the studio than on tour? Let's use James Brown as an example. I wonder if Tim Drummond played all the bass lines from the Bootsy era just like Bootsy when he toured with JB. If he didn't would the band be doing it wrong? If it were different, could it really have been an improvement on what one of the most influential bassists of the Funk era did?
I was joking.
An "improvement" is such a personal judgement I wouldn't even offer it as criteria for what constituted a legitimate performance... then again, I didn't offer it so all is well.