Can I find statistics on the number suffered death and failed or repeated missions in Assassin's Creed 3? Whether such factors are not measured anywhere?
While in game (in single-player while in the Animus), go to the pause menu and open the Animus Training Center.
There you can see your personal statistics in the Stats menu or see how your stats fare against your friends or the world in the Leaderboards menu.
Another option is to log on to the Assassin's Network where you can keep track of your Assassin's Creed progression across all titles, participate in the community by forming clans, and fighting in events for great prizes.