I think it’s fairly well established that guitars can and do change with time. Why and by how much is still debatable. I wouldn’t expect the main resonances to change more than a semitone in the lifetime of a guitar but there is certainly some settling in of a new instrument. I say the wood is ‘learning to be a guitar’ but who knows what’s really happening? There is much received wisdom about ‘vintage tone’ in guitar circles but I don’t see why a guitar should necessarily get ‘better’ with age ...I wonder if time spent in certain environments can change the behavior of the body so that a guitar that tests well in final QC at the factory could develop such a thunk.
That said, I built a guitar a few years ago that I wasn’t very happy with. Oh well, shit happens ... I took it out the case recently and it sounded great! Placebo? Wishful thinking? Did something actually change? I really should do some tap testing on it to see what’s going on, if anything ...
In recent years there has been a fashion for using ‘baked’ or ‘torrified’ woods in guitar making to emulate the effects of age on a guitar. There is some evidence that the volatile components in some woods oxidise with age and the lignin hardens resulting in wood that is more resistent to humidity swings and is both lighter and stiffer. Torrefaction seems to do the same (it’s a technique loaned from the hardwood flooring business). Does this result in instant vintage tone? I’m sceptical. However, I tried tried baking a top in the oven for fun a while back. It came out a bit toasty (and the house stank for days!) so I used it in a dark sunburst copy of a Gibson ‘Robert Johnson’ style L1. It’s probably my best sounding guitar. Hmm, is this due to the baked top? Consummate skill? Luck? Who knows …? ;-)