If we want to honour the definition of GTFS, then we must use ref:STIB_MIVB=5 for this station, but then we’ll lose existing information, which I think is the correct one.  (IMHO, the mistake comes from STIB/MIVB’s export which spawns new id numbers for stations when generating those files instead of using the established ones.)

Please leave me a few days to consult two fellow mappers who work with GTFS, and we’ll see how we fix this issue.