Whenever you go and remove the “primary thumbnail” for a game’s place… (primary being the first thumbnail in the carousel that is used for home-page recommendation)
… the thumbnail annotation will indicate the removed thumbnail as the latest one set rather than the one behind the primary in the carousel which would become the primary thumbnail in this case of removing the primary.
Page URL: https://create.roblox.com/dashboard/creations/experiences/[GAME_ID]/places/[PLACE_ID]/thumbnails