I'm kinda confused here with exactly what question you're asking - but I'll give it a shot... here's a quick rundown, maybe this will help.
99 to 04 seat pans were wider and made from a very hard plastic, they had numerous other subtle differences from 05 and up pans as well:
1. Rivets were used to attach the vinyl instead of staples.
2. The adjusting bar on the bottom had more space between the high and low settings.
3. The H shaped hold down clip on the back had correspondingly more space.
4. The taper toward the front of the seat was wider, making it a bit harder to get your feet closer to center line at a stop.
5. The foam is softer and thinner.
6. The foam is shaped differently
7. The lumber support is thinner, so that you sit a bit farther back in the seat.
8. The vinyl has a grain.
9. They were only available in black, not gray.
10. There was no stitching in base of the seat cover.
11. The design of the bottom of the pan was completely changed in 2005 and later years to allow it to sit lower in the frame, effectively slightly lowering the overall seat height on either the high or low setting.
11. "Soft Touch" seats were only available as an option, since about 2009 ALL seats supplied by BMW were "Soft Touch".
12. The pan material was switched in 05 to what I call a "fibertech" material and staples were used to attach the vinyl. Some were a greenish color while others were black.
13. "Soft Touch" seats - no matter what year - are kind of a cruel hoax. The only
difference between them and a standard seat is a 1/2" layer of VERY soft polyurethane foam that makes it feel more plush when you touch it from the top with your hand. It does absolutely nothing
to make your butt more comfortable since it compresses completely flat as soon as you sit on it.
14. 99 to 04 seats and 05 to 10 seats cannot be easily switched back and forth since there will be some interference with the plastic side panels, which will need to be hacked in order to get a snug fit. There is no difference in the side panels or frame, it is all in the design of the pan. I no longer make specific recommendations exactly how to do this since the end results are usually pretty ugly - no matter what your skill levels - and I don't want to be blamed for ruining someones bike. (It's happened...)
15. All of the passenger seats and trunk backrests are identical from year to year.
16. 99 to 04 seats are considered to be a bit more comfortable seat since they are wider and offer some lateral support. Pretty much all of them are not suitable for riders above around 200 lbs. since the foam compresses easily.
17. The change in design in 05 is attributed to many potential purchasers complaining to dealers in the showroom that they could not reach the ground easily even on the low setting. It looks like BMW has dramatically over compensated this with the new GTL and offers a high and low seat, but my bet is they will both be very uncomfortable as usual - and a big thank you to BMW!