IMHO, the "1/11" case is simply an incorrect tag and you shouldn't have to code around it.

Unfortunately, it isn't an incorrect tag at all. From the ID3v2.3.0 spec:

TRCK: The 'Track number/Position in set' frame is a numeric string containing the order number of the audio-file on its original recording. This may be extended with a "/" character and a numeric string containing the total number of tracks/elements on the original recording. E.g. "4/9".

The "/total" extension to the TRCK field is actually done by most ID3v2 taggers I've used. So you really do have to code around it, if you want to use the ID3 tag to determine the track number... However, using the playlist position field as Tony suggests is probably good enough for most people. Personally, since I tag all my own tracks, I trust the ID3 tags over any data I might get out of the Empeg's database.