Wow, thanks, that's just what I was looking for. I did a quick survey around Alioth to see if I could test this and
almost validated what's in the article. I took the data and sorted it by stellar mass (there's also a load of other data I collected in case it was relevant), note that I haven't found any K stars with sub-class of B (yet). The article seems to be based on some pretty solid astronomy knowledge (mine is pretty minimal) so my findings might show a slight error in the classifications in the game (if I have this right).
My results below:
If we assume that 'whereas “ab” is somewhere in the middle' suggests that FD may have sometimes used AB for a middling sub-class and sometime used no sub-class to mean the same this appears to show the mass is back to front. Note that the sub-class "A" is associated with the least massive stars but according to Professor G this should be the most massive stars.
I've yet to see a B in K class but I found an MIV which could help if I can find another MIV to compare it to. I'll post an update if I find out more.
For now, this pretty small test appears to show that when dealing with an unexplored system in ED - an "A" suffix denotes an untypically small star for its Class, a "B" suffix presumably denotes an untypically large star and "AB" only tells you that it is neither "A" nor "B" and is more or less the same as having no suffix.
I'd welcome any more comments or insight.
For anyone wanting to go straight to the original article - this looks to be the boy
http://www.firstgreatexpedition.org/mybb/showthread.php?tid=1455