Do you mark articles older than 30 days as read?
Yes. The reason behind this is that we need a reasonable limit to be able to compute unread counts in sub-seconds. All the articles stay in Feedly indefinitely, they are just being marked as read.
2 comments on this:
1. For feeds that publish less frequently but that you still want to follow diligently, there is a preference setting in Feedly to mark certain feeds as "Favorites", this may be a useful feature for this purpose: https://feedly.helpscoutdocs.com/article/262-how-to-move-a-source-to-favorites. Articles in Favorites will still be marked as read after 30 days. Marking a source as a favorite is just a way to make sure you don't "lose" new articles from sources that don't publish often.
2. Just in case this isn't clear: you can still access the entire feed history we have indexed in Feedly over time by setting your feed preferences to display all articles (read and unread). To set this preference, see: https://feedly.helpscoutdocs.com/article/264-how-to-show-both-read-and-unread-articles