Late arriving hits can also have an impact on historical reporting, though it's typically very small.
I've seen it most often with apps. For example, a session ends abruptly and the app doesn't send the analytics data before shutting down. I believe once the app is launched the next time (which could be several days later), that previous analytics data is sent. Once Adobe receives the data, it will increment for the correct day based upon the event timestamp (not when it was processed).
If you're seeing very slight increases, I'd expect it's due to late arriving hits. If you're seeing significant increases, I'd suggest to start by validating late arriving hit volume. If you have data feeds, you can enable or disable the sending of late arriving hits. Either way, you can determine the impact. There's more info on this page.