Any chance you kept receipts? Or paid by cheque or CC? Then check your account statements for the amounts. You should be able to reconstruct a fair amount, if not all, of the flights you did. You could enter a Stat. Dec. in the log book to cover the missing instructor authorisation and/or try to get hold of your previous instructors to get them to re-do their entries. If you do manage to contact past instructors, their log book(s) will also have your flights in them so you could copy from them, too.