Ah, mystery solved. Mark Anderson just emailed me that the September archive wasn't resolving. Couldn't figure that out, since the file was there. It was the individual permalinks that were malformed in the file, and therefore everywhere else. Like the RSS feed.

"Yay for automation."

Well, yeah. If it does everything. Had a template assignment glitch initially. Caught that. Did not detect that the "permafile" attribute wasn't being set. Had to go back and fix that. Fortunately, the RSS feed already downloaded in NetNewsWire had all the correct creation dates since I foolishly corrected it by just dragging the posts out of the September 2023 container and dragging them back in, which had the effect of giving them all the same creation timestamp. Alas.

"Switching to manual!"

Fingers crossed, all should be well. The apocalypse has been postponed.