TDZ is always controlling, MID and STOP END if reported and relevant. It then defines what is relevant ie >60kts. So the TDZ RVR has no speed limit before it is controlling ie it’s always controlling - I think we agree so far. However, if it’s not reported due to an unservicability then it cannot be controlling. There is no mention of replacing other reported RVRs, which themselves have alternative limits anyway.
The approach ban allows you to continue an approach below 1000’ no matter how low the RVR has fallen, assuming it was ok prior to 1000’. If you have sufficient visual reference you may land - the actual RVR at this point is irrelevant. Would this not be similar to a failure of the TDZ transmissiometer? So long as the MID and STOPEND are within limits (if relevant) you attempt the approach and if you have sufficient visual reference you may land, if not you goaround in the time-honoured fashion ?
That it was once written differently in your FCOM could be that your airline have chosen a more restrictive approach which is always allowed.
I do believe that many of the regulatory documents have scope for interpretation, hence the addition of AMC and GM sections. Unfortunately not so in this case.