Just want to add as it is NOT readily apparent (I didn't notice til it was pointed out to me by another member)-- but EVERYTHING required for 100% on the social club page has a thin colored line on the left hand side of the icon. Each section has a different colored line for this (they correspond to the color of the stats bar at the top).
The only section that does NOT have a line is the "random" events-- this is completed by doing any 14 random events.
Example is below-- you can readily see from a screenshot from my page that I still need to complete the third triathalon-- but if you look below-- you will see a few other events without the line which indicates they are NOT required for 100%.
It is also worth to note that the social club page will be updated when you are online and save the game-- if you happen to load an earlier and save-- it will updated the social club site and only show you having done whatever was done on your latest save.
With few exceptions, the social club syncs right away when you save your game-- I've been in the 100% hunt and quick save whenever I complete a requirement and check the page immediately to make sure it counts and it is almost always there (other then about 10 days ago when it was taking up to a day to show things up)