Find out the following if you can. Where did the fingerboard come from and how "aged" is it. Then, at what RH was it constructed into the guitar, and how does that compare to the RH where you have it now.
My guess is the wood is shrinking, not just from RH of it's environment, but from the aging process itself. There is something to be said for aged tonewoods and proper RH when used to construct the instrument.
Knowing a bit about the maker, I find it hard to believe he'd use unseasoned wood. It's fairly common for supply houses to kiln dry wood these days, which is not the same as air dried through many RH cycles.
Our rosewood and ebony was kiln-dried over a ten day period, but in a land where the humidity is 80-90 percent, so I'm sure it took on RH water after the kilning process. Aging is not a bad thing, even if it has been kiln dried.
I wouldn't worry though, sounds like the guitar may require a little rework on the fret ends. Not a huge problem, any competent luthier, such as yourself can handle that.