Maybe they have some ruined samples that can be sacrificed... that’s all I can think.
I’d bet it makes little difference what they were finished with, and more difference what the ultimate dimensions (including the thicknesses) are. Sometimes violin makers find that the unfinished instrument sounds better in testing, but they can’t leave them that way as the wood would deteriorate.
****I’d bet it makes little difference what they were finished with, and more difference what the ultimate dimensions (including the thicknesses) are****
The finish on acoustic instruments has a significant part to play(no pun intended...ok it was intended)in the final sound of an instrument. For example, a clear finish and a satin finish will make identical models sound different(less brightness for the silk finish).
Between the finish and the age of the original Stradivarius, it will be difficult to match the sound even with correct dimensions and woods. Also the sound of those Strads has changed over the years, so nobody alive today really knows what a contemporary instrument really sounded like.
Of course these are small differences and not very noticeable to most people, but the players can easily tell.