Can't get author name to show on post

We migrated an old site to a new install, and the posts were added with the default admin user so they showed the current date and admin username (because GoDaddy created the user without asking for a first/last name). Note: I know we could have just moved the code and database over but a clean slate was better and there wasn’t a lot of content.

So now that we’re backdating the articles, I can change the author but it’s still not showing the author first/last name after I added it. Any post that was created with a user that had a first/last name shows that author’s first/last name.

If I look in the database, the posts table post_author column just shows an ID number; I don’t know what to change to get the selected author’s name to show up if the article was created before the name was added.