I believe that Ansel once said that if he got one really fine photograph a month, he felt he was doing well. So if you calculate the time that you feel you have left to you, shall we say ten years, then you might get another 120 really fine frames. Well, how many superb pictures do you need, for heaven's sake? I think 120 would be enough to leave to posterity. How many great photos can you call to mind (quickly, mind you, and no cheating looking in books) of Weston, or Adams, or HCB, or Brandt, or whoever - a dozen or so, perhaps. This is not something to agonise over. Most visual artists have drawers or portfolios full of stuff which did not make the grade, as well.