With M900 (the first of the superlow profile cranks), there was 107 and 113 UN90 bottom brackets designed for it.
This was quite different to the (121)122/127 that had been used previously.
Here's the 1993 UN91 listed, but is pretty much the same as the '92 I've not put in the archive yethttp://www.retrobike.co.uk/gallery2/v/M ... ewsIndex=1
Now I don't know why 110 where created or when/what for, but it's an in fill and moves the non-drive side out by the few mm. I guess as some setups for possibly the new M737 etc needed the extra length there.
I guess it does also give the option of adding some 0.5mm/1mm/.. spacer on the drive side to tune chainline if you so desire.
It's possible it's for the medium band, but then people have shown as mentioned above the length is all on the non-drive side.