What did Canada mandate, being the country of design authority?
Didn’t TC owner Viking Aviation issue a bulletin, perhaps even call operators?
I think at Pacific Western Airlines we’d have inspected horizontal stabilizer structure and controls after reports the aircraft dove into the water, and again when NTSB revealed what it found in the wreckage.
And any operator should especially inspect any Otter that was maintained or overhauled by the same people as the accident aircraft.
Long shots but preventing such accidents is essential.