Boeing Eng:
"....Puzzling to see the Tridents (thought they were CAT3B by then)"
Don't forget that although the aircraft might be certificated for CAT3B operation, that assumes that ABSOLUTELY EVERY component in the system in that specific aircraft is fully serviceable otherwise it is downgraded to CAT1.
Don't forget that every member of the crew has to have been trained in CAT3B operations and also has to be ABSOLUTELY CURRENT to be allowed to operate to CAT3B limits.
I never flew the Trident but it has happened to me on other aircraft that I have been screwed because the aircraft and I were fully current but the first officer was not.