Bottom bracket spindle lengths nomenclature

[rrarider]

Having bought a wrong sized BB spindle length a while ago, I know how important it is to measure the one that currently fits and order the correct length for a replacement. I'm puzzled by the markings I see on a Shimano un55 packet, namely:
107 : ( M107)
110 : (M110)
113 : (LL113)
115 : (D-H)
118 : (XL 118)
122.5: (D-NL)
127: (D-EL)
The ones with digits in I could probably deduce myself but the alphabetic only codes seem most unintuitive. Is there some standard coding for BB spindle lengths that has somehow escaped me?
I ask because whilst looking on ebay for a spare one to have available, I'm surprised to see so many listings for used BBs that don't quote a spindle length. As a secondary question:

I know that the current 127.5mm BB fits my bike perfectly and I've just made a bid on a 127mm BB, assuming that the half millimetre difference can easily be accommodated by a bit of limit screw twiddling?

All answers will be gratefully received.

 

[Cycleops]

Don't really see the problem, if you want 127 that's what you should order. Shops usually give that option on their sites so best to order there.
As far as I know 127 is the standard on UN55 bbs so likely the seller has made a mistake unless a different make but . 5 is not worth worrying about.