A Cat III approach without rollout guidance for autopilot is flown with Cat IIIa minimums.
Unless there is a note preventing all Cat III operations.
If the approach has Cat III rollout guidance, it is a CAT IIIb approach.
Boeing 747 classics can be certified to Cat IIIa... but not Cat IIIb.
Yet their autopilots were capable if they had that option, but never were certified.
xxx
Happy contrails