I am very much in the "if you can't be bothered to learn the words, shut up and let somebody sing who could be bothered" school, and at one time, I too had a large repertoire in my head of 200 or so. Most of them are still there, but occasionally I get asked to sing something I last sang forty years ago, but can't drag it out from where it's hiding.
My current answer is to learn it again, but as my memory is imperfect, and - quite frankly, I no longer have the time to produce a new song each week, as I used to - my answer is to print off a version that I think I know and amend this until it is the version I think I knew, and learn from there. But Shhhh! I stick the printout in my pocket as a memory aid for the odd word, or line!

Chris B.