Back-dated items not appearing after "Mark All as Read"

NewsBlur folder for the journal Nature:

I noticed that I was only being shown maybe a dozen items each week in this feed, while the site statistics report about 400 per month / 100 per week. Also a lot of things marked unread that I don’t remember seeing, and often things that I probably would’ve read. So I saved a copy of the RSS XML file each day from June 23 to June 29, to compare new items in the feed to unread items shown in NewsBlur. (I’m not sure how to do attachments here, but would be happy to share the XML files if someone gives me instructions.)

It turns out that the journal back-dates items in the feed. Comparing the XML files from today and 24 hours ago, this morning there were 43 new items in the feed. 3 of them were dated June 29, the other 40 were dated June 28. Yesterday (June 28, about 17:00 UTC / 8am PDT) I clicked “mark all as read” in NewsBlur, and this morning only the 3 dated June 29 are displayed as unread.

The XML items contain date stamps but not time stamps, eg, 2023-06-28. NewsBlur appears to interpolate this as 00:00 UTC June 28 (5pm PDT June 27), 17 hours before I clicked “mark all as read.”

Somewhere in the past week I tried individually reading all the items (hitting j a bunch) rather than the “mark all as read” button, and back-dated items appeared correctly. I didn’t take careful notes of that, though.