I think Keios has it right: there were two Comic 614s posted by mistake, and so only one was put in the archives. Ditto the other comic.

On a related note, since you mentioned having all the comics since 340 still stored on your computer earlier, I'm going to go through and see if there are any others missing from the archives after that point. 351 is the only one that stood out to me when I originally read through them, but there might have been a few others.