Della no incorrupt saint I know of is perfectly preserved or unblackened and does not slowly deteriorate over time. Unless you can reference source material other-wise I think it best to stick with what is generally known and accepted.
Original descriptions of those exhumations even back in 1925 noted areas of skin were missing for example.
“The body is practically mummified, covered with patches of mildew and quite a notable layer of salts, which appear to be calcium salts. … The skin has disappeared in some places, but it is still present on most parts of the body.”
(Source here)
The use of wax wrt incorrupt saints appears tro extend beyond a thin, transparent protective coating. St Bernadette’s body seems to be no exception. She has a solid, moulded wax mask because authorities did not want the blackened face and sunken eyes/nose to disturb the viewing public. Her skin despite that was well preserved on the face. Her body does appear to be one of the best preserved.
So “incorrupt” is pretty much in the eye of the beholder. Does that detract from the sanctity of the saint - I don’t think so. As there are apparantly numerous cases of incorrupt exhumations wrt persons of other races/religions it seems we have to accept that there may be causes other than divine predilection - or that sanctity is not monopolised by us Catholics.