More generic letterhead recos are useable, but it's just harder because the writer may not answer all of the questions asked in teh reco form. If you can read the letter and know that there are some important questions in teh reco forms that go unanswered in your letters, then I would advice against using them. If you can do it ahead of time, read the reco forms from your target schools and try to make sure that your recommenders cover these questions in a single letter.
If you reapply, adcomms will sometimes take portions of your previous app into account. How much they use your old app varies by school, though. I recommend assuming that they will NOT look at your past recs, and making sure that anything important is included in your new ones.
Scott
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Co-Author, Your MBA Game Plan