Hive is a fork of Steem (the blockchain), not Steemit (frontend to the blockchain and/or company). Any posts before 2020-03-20 are included in both Hive and Steem since they share the same history. Any posts after that date are on either of the chains, depending on from which interface you post.
Yeah, I was thinking about the frontend more at the time, but this is another place I'll be posting to in any case, seeing as I already have an account here, and it lets me see how things progress on here.
It does seem easier to set up additional accounts here though, which is handy, as I have another account I want to deploy here, that's a totally different focus to this account!