Precision Approach- As long as your visibility/RVR exceeds the appropriate minima for Cat 2 or 3 by the OMK or 1000' AAL, whichever is appropriate, then you may continue down to appropriate minima and disregard any other visibility reports, even lower than your minimum visibility for that approach.
For a NPA, an 'approach ban' excludes ANY approach? My understanding is any deterioration of visibility below your minima requires either not commencing the approach or a go-around. The minima are higher for a NPA, so the time between the OM/IAF and Decision Height is very short and not worth arguing over! It's academic.
Be reminded that cloud base is not included in the above and may be disregarded.