Yes, you are stretching it a bit.
Small changes may have been made in restored paintings, and big chunks may be knocked off Greek marbles, and bits of mosaics might be reconstructed, but that isn't the point. There are plenty of pieces of very old artwork that have been perfectly preserved and would be recognizable to the artists, even after four hundred years.
Note that when the Koreshoffs sold off their trees, it was with the understanding that the trees not be credited to them in the future. Their feeling was that the trees, under someone else's care, would no longer be theirs. As old and refined as those trees were, the new owner not only could not, but MUST not call it a Koreshoff tree. Interesting.
Joanie