I think you are good on the history. More than I had. My boat had an intervening owner who spent a couple years finishing the woodwork before deciding, or have his wife decide for him, not clear which, that it was best to abandon the project. He did pass on a few receipts.
If the story with the sails matches with their actual history, then you definitely came out ahead. Sail numbers may even be correct. If you sign up as a DSA member @dsssec can verify that the number isn't claimed by anyone and "assign" it to your boat for purposes of class racing (or vanity). She, or her predecessor did that for me when I bought new sails and felt like having a number on them would be the thing to do.
Not soon after, somebody gives me an old spinnaker, and now I sport two numbers ...