To me, "Here ends the Epistle" would only make sense if you were reading a whole Epistle (and Corinthians is pretty long!) or a passage that happened to be at the end of one.
Good point. But I remember from my youth that it was common for people to use that phrase if they were reading from anywhere in an Epistle. Perhaps it is or was understood to mean "Here endeth the Epistle reading." But you're right in that the way it reads, it's as if you've read the actual end of the Epistle.