Of course, another intriguing possibility is suggested here. This is that the fast of the Seventh Month is either inspired by, or developed in competition with, the annual fast of Yom Kippur. Here is some lectionary evidence provided from that source.
Instead of "epistle" the tables should note "lessons" (of which there are six on Saturday). The final footnote highlights the fact that the peculiar events of this gospel lection (for a Sabbath) "leads to a discussion on the meaning of Sabbath."