Eric:
Noticed this evening that NH 129 is signed to the west of NH 106 in addition to the normal segment to the east. I did not have time to investigate this in the field, but the signs I saw are similar to what appears in 2013 GMSV. OSM seems to think that it extends all the way west to I-93/Exit 17, though I doubt that's the case. 2013 GMSV shows signage beginning on the south wye of the Village Rd junction in the middle of Loudon, so not far west of NH 106.