I think that I did the same thing- sent recommenders a generic form, and later, filled out forms for them. I emailed LSAC- apparently that waswrong and can cause a mismatch. One I made inactive, which I hope will help, the other, I was able to delete.
Still waiting to find out if this was the correct move.
Fortunately (hah), neither had finished their letters at that point, much less mailed them.
Here's the email reply:
The letters will still be processed, but may not be matched to the listings you have created because the barcodes will not match on the forms. Once you receive the confirmation email for the letters, please check your online account.