Somehow, I had one version of my Mii on my Wii, and one version on my 3DS. When configuring my Wii U, I used the 3DS version, since that was the only one I could import on initial setup. After importing Miis and save data from my Wii, I then deleted the duplicate version of my Mii that had been copied from the Wii out of the Wii U's Mii storage.
However, I noticed now that when I boot up Super Mario Galaxy 2 on my Wii U, my save file just shows Mario, not my Mii. Did I accidentally delete my Mii (and thus any Wii Sports save data and any other Wii save data that requires a Mii) from my Wii U's Wii menu as well as from the Wii U's own Mii storage?