There are some services like Feedly that cache everything some users did use, so you can go backward even if you subscribed just now, but unless someone usees i

There are some services like Feedly that cache everything some users did use, so you can go backward even if you subscribed just now, but unless someone usees it, I doubt it will work as it implies service must crawl internet for RSS feeds and subscribe to them all the time in order to keep history (since RSS on its own can't do that). Sounds like internet archive for RSS.