So I walked the stretch between Garnlydan and Brynmawr today and its odd. There are signs on nearly all the minor forks on the path but the signs are missing for all the major forks. there's even no signage at the east end nor at the ramp from the B4560 where I entered the path.

There is also a information board near the A465 highest viewpoint which has a simple map on it show amoung other things, NCN paths, it seems to show the south path of the 46 along with the 466 but not the north path. 

The sign post at the viewpoint also marked as west from the viewpoint as a "local cycle route" and east as part of the "Ebbw Fach Trail" but no mention of the NCN route. 

I think my original theory still stands and the north route was meant to be removed but they skipped the majority of the harder to get to signs. it also terminates literally in a garage's storage yard and doesnt really go anywhere. however since we map what's on the ground if you have no objections i'll remap it as a separate link route rather than a alt path of the main route. I think this makes more sense since it a dead end and I suspect they will remove it eventually.

I'll also look into this Ebbw Fach Trail since its seem rather extensive and well marked. the map indicates that it extends all the way down to Aberbeeg.