The DCIM folder layout and naming follows some standard (forgot which one), which states that the files are of the form
AAAA being four characters, doesn't really matter what
XXXX being four numbers, must be unique unless the files belong to each other (AVI + THM, for example)
EXT being the extension, of course.
So there is really no way that the camera produces a file, in the DCIM folder, which doesn't pass validation in this way. Granted, it's probably not the best way but it works.