http://en.wikipedia.org/wiki/Vermont_Route_100#VT_100B suggests that 100B is the spur and there is no indication of a 100Bus. Also the only segments I found were from one editor so I suspect that person did not research this before editing the name. All other, correctly named, segments are created/edited by others. I would guess your change would be appropriate.
Re: State Rt 100B is labeled as 100 Bus