Technically, it is the local VTR Chapter that hosts a VTR "National" convention each year. In 1993, it was TYEE Triumphs; this year it is Southern California Triumph Owners Association (SCTOA) hosting the combined VTR Convention/Triumphest.
As for the anniversary year, it depends on who is celebrating. The year 1952 has also been celebrated with various events, that being the year that the Type 20 Sports (later nicknamed the TR1) made its debut.