We have no control over RSS feeds. It is very common for them to only allow downloading the most recent 10, 20, and sometimes (but rarely, in my experience) 50 entries. This is entirely dependent on the publisher of the feed.
Is there a way to bulk download multiple linked articles on a webpage? For example, here is a blog that I’ve added to my RSS feed for the future, but which also has a archive in one place with every previous article. I’d love to download all those previous items as web archives.