Well, I've just got bad news regarding my last thousend DNGs from Phil Harvey, the develepor of Exiftool:
"The problem is that the camera is storing an incorrect value for the
SubIFD1 preview image length (tag 0x0117). In this image, the stored
value is 115200, but the length of the JPEG preview is only 93416
bytes. Trying to read the full 115200 bytes runs into the end of
file, so ExifTool reports the error and won't write to this image."
Now I don't know if the incompatibility of my camera and ASP lies in the wrong file format (as the DNG format is supposed to be a standard file format) or would it still exist without the error.
I've written to Ricoh now, wondering what the answer will bring.