Aaah, wail & sorrow! It was ME who was wrong. How could that ever happen?! I just received the receipt of the book I bought today, and forgot that one of the books I bought came from Feedbooks, because Kobo didn't have it.
Thus, 105 at Kobo (one of which was bought today), 2 errors with PayPal, netting 107 mails from Paypal. Check.
1 book at Feedbooks, creditcard, no Paypal mails, 1 receipt. Check.
105 Kobo receipts. Check.
Everything checks out, and randomly checked Kobo receipts all have the correct discounted price.
Now please excuse me. I'm going to spank myself for miscalculating.