There might be another reason not much difference was heard. That reason is that most of the musicians were incapable of eliciting the full potential from said instruments. My ex-girlfriend was also a professional violinist performing mostly as a Soloist (doing among other things 24 Paganini Caprices all in one setting on several occasions). During our 4 years together she had a number very highly regarded instruments (one Strad, one Guarneri del Gesu and a Guadhinini) each of which sounded radically different in her hands. She told me once that of these the Strad was the hardest to play correctly but was the one capable of the highest performance (it apparently was very demanding on perfect technique). So it was quite possible to get merely mediocre sound from these instruments if not in the appropriate hands. Now that is not to say the musicians in this orchestra are bad, far from it, but maybe they don't have the skill to get the most out of thoroughbred instruments. She also had a cheap Romanian violin on hand once because a friend of hers was trying to sell them here. It sounded like it looked like, a box of wood with some strings, no tone, no life, nothing. The sound from the Strad literally exploded into the room. This one instrument could easily make my ears pulsate as it pressurized the room! It had much more of this effect than any other instrument she had even though the others were quite impressive as well.
Do not confuse production of music with REproduction of music. You are correct that the production of music varies from day to day, venue to venue, etc. etc. However; if I record you live in Carnegie hall playing a Strad and then play it back at home it damn well better sound like you playing a strad in Carnegie hall. If I can't distinguish the hall signature or the tone of your instrument as a strad (assuming I am attuned to this in the first place) then either my stereo lacks accuracy and resolving power or your playing sucked and you made a Strad not sound like a Strad. However; I should have heard this when I made the recording so I should know what to expect. You live with the sound you make and listen to many others playing all the time. Therefore, you should have a good grasp on what is "correct" sound. If a stereo makes all violins sound the same and all halls sound the same then it is WRONG. My ex was extremely quick in telling if a system was even close to correct in sound. If it was off significantly she couldn't tolerate it for more than a few minutes.