The adds don't pop up throughout the game. 3 adds appear in the message board at the start of a game file (after the loading screen). Once you exit out of them, they don't reappear, even if you go from Sunset Valley to University, for example, they won't reappear once the loading screen is done. From my experience, they only occur after the loading screen between the main menu and a game file. I'm not sure if they'll pop up if you go from file, to the main menu, and then back into another file.