How what kind of backlog will it keep for unread items? It's not that weird for me to not pay attention to a feed or collection of feeds that I don't have time

How what kind of backlog will it keep for unread items? It's not that weird for me to not pay attention to a feed or collection of feeds that I don't have time for at the moment. This is one of my main issues with newsblur, which has a ridiculously low limit of 500 per feed max (based on the number of subscribers the feed has), if you aren't a paying member and it's a low subscription feed it could be as low as 25 posts or something.