Thanks for all the help and information. In experimenting with a simple NSF header detector, I discovered a few cases where duplicates were generated due differences in the actual header.

For example, the NSF header (http://tinyurl.com/yznzln) contains certain load/play/init adresses (0x0008) and a region setting (0x007a) which controls playback frequency. Sandwiched between those two important pieces of data, are the label fields (0x000e), which often vary considerably.

Because certain .nsf files can have their load/play/init addresses or region setting corrected, while the data segment(0x0080) remains the same, I am left with duplicates. Someone rebuilding to this DAT could think they have the correct/fixed version, when in fact it contains the wrong load/play/init addresses or region frequency.

So...do you (or anyone) know of a way to skip a portion of the header, specifically the labels, while retaining the load/play/init addresses and the region setting? It seems that the current implementation of the header detector can trim segments from either end of the file, but not (to my understanding) remove a chunk from the middle of a file. Being a "header" detector, this makes sense, I'm just hoping someone has a trick that could help me solve this particular problem.

I have included my NSF detector here as a reference (http://tinyurl.com/v6pbv) for anyone that has some ideas.