Perhaps I should clarify
On my account, I merged my initial discourse admin account with my imported account from the older forum. All the topics I have ever posted in correctly show up on /posted
For everyone else, the account they are using was only imported from the old site. For them, only topics they have posted in after the import show up in /posted. I have confirmed this using a test alt account I have
I assume that imported posts should still matter when it comes to what shows up on /posted, so the behavior is correct for my account but not for all the other users. I’m assuming the merge step is what did it because that assigns all my old posts to a new account AFTER they have been imported