One of my bandmates recently traded a viola to another part-time/interloper bandmate - about 3 months ago, IIRC. It was originally built in 1835 or something, but has undoubtedly had work done on it in between.
Anyway, the first bandmate wasn't using it - she plays fiddle (violin) but not viola, it was her late-husband's instrument, so it was unused (sitting in a case, I believe) for probably over five years, maybe more.
Over the last month, the viola has really sweetened and filled out in tone. I don't know whether it is from human sweat/oil interacting with the wood/strings, or the strings being used after being dormant for years (I honestly don't know if it was restrung as a result of the trade), but everyone agrees it was "sleeping" and it is now "waking up", and every time we play with the new owner, it sounds better. Maybe it is just a case of the new owner getting used to the instrument, and finding the tones that were always there. :dontknow:
Apparently this is common with quality-built traditional wood-based acoustic instruments - violins, violas, cellos, etc. I don't know whether it applies to "instruments of considerable age" or would apply to a new-built high-end instrument. I strongly doubt it would apply to an entry-level factory-built violin bought for a few hundred bucks.
I also have no idea whether the same concept applies to modern-built quality acoustic guitars like PRS PS/Core Tonare or Angelus guitars or even the more cost-effective "productionized" SE Angelus line.
yay! More anecdotal evidence that may have no connection to reality!