IMO, the answer should be that paths A and B are valid - both for a normal rout and for using Low Crawl. Using Low Crawl pretty much determines that the unit will NOT reach its destination during the RtPh, which makes stipulations regarding MFs spent kind of moot.
Since the first sentence of A10.52 already states that MFs will not be at issue in a Low Crawl (since it will use all of them), the operative factor is cited at the end of A10.52:
All other Rout provisions apply unchanged to Low Crawl, e.g., rout must still be towards the nearest woods/building Location within 6 MF.
The "other provisions" will still require a LCing unit to select the closest destination in MFs (BB1), but the path will no longer be MF dependent (as per the following EXCeption):
A10.51 ...At the start of its RtPh, a routing unit must designate its destination and must attempt to reach it during that RtPh [EXC: if using Low Crawl].
Both A and B gets the unit closer to BB1, both require the same # of MFs to be spent (ALL of them).