I have several lacquer cracks mainly running from the bridge on my 2002 D50. I bought this last year and had been really played over the years and not really taken care of very well (I don't think the fretboard had ever been cleaned etc.)
so I assume the cracks were due, in part, to poor storage but maybe I was wrong?
i'd say the ones running along the grain lines were likely started by the underlying wood beginning to separate due excessive dryness. Combined with NCL's natural shrinkage as it ages, the cracks follow the path of least resistance along a grain line. The curved one by the 'guard looks like a more typical example of pressure or temp shock checking. In those cases the NCL behaves like glass, just like a windshield crack that wanders randomly.
RE poor storage, it could have had a contributing effect if the guitar was never cased (and Coronas came with cases as part of the package), and lived in a dry climate like the southwestern desert.
Keeping 'em cased slows down the outgassing aging which shrinks/makes the NCL thinner. UV from sunlight also degrades it but imparts a gradual ambering up of the NCL over time, too.
If you put my D25 ,which spent literally hundreds of hours outdoors, next to the D40 which has only been out of the house 4 or 5 times, the D25 looks like it actually has an amber finish, while the '40 which has virtually never been exposed to direct UV and spent much more of its life cased, is still almost as "white" as when it was new.
The '25 was always cased when not being played too, but it's showing the typical finish shrinkage that runs along the grain lines: the NCL gradually starts to conform to the texture of the high and low ridges. But no actual separation. The '40's just barely starting to show that shrinkage along the grain lines.
Note I've owned both of 'em since new so I know the complete histories of each one, making for a pretty good A/B comparison of finishes. Also the '40's finish was a LOT thicker than the '25's from the start. I'm also lucky enough to live in a place where the humidity is normally in the ideal 45-55% range almost all year.
