Only six items available in a specific feed (missing dates?)

The feed at https://useoptic.com/rss.xml , when added to Newsblur, only displays 6 entries (“Writing Lenses” through “Workflow”), no matter what display options I choose (oldest to newest etc.)

Importantly, Newsblur doesn’t display the “What’s next for Optic” post from 17 Jul 2018, which is the newest post. It makes me unsure if newer posts will show up in Newsblur when published…

I checked https://validator.w3.org/feed/check.cgi?url=https%3A%2F%2Fuseoptic.com%2Frss.xml and while it doesn’t validate (1 error and a few warnings), it doesn’t seem to show any errors in the affected entries.

While writing this, I noticed that the first 20 or so entries of the feed (before the “What’s next” item mentioned above) are missing the date (when looking at the feed in Firefox). I can imagine how it causes the behavior I’m seeing, but:

  • I’m still not sure if new (dated) posts will show up in Newsblur (assuming the dateless items remain in the feed) or if I need to contact the blog authors
  • If Newsblur showed all the entries from the feed, I wouldn’t be compelled to write this question.