Good question Pete.

The answer is, on AC/DC you can see by looking at the back panel on the back of the playfield at the jukebox, the songs u have played will be lit already on the song selector.  I am pretty sure/certain that is correct. The game does allow you to chose a song again that u have already played so u can increase your score on that song, therefore making yourself the grand champion of that song, making it harder for someone to beat your song score.

On TRON, I have to play it more to work out how to get the best out of that game as well, but by watching all the STERN videos on their site, it does make it easier to work out how to get the best out of the game. Admittedly, some of the new code changes on different games are not reflected in the videos, but there is still alot to learn from the videos. I even learnt alot more for X Man watching the X Men LE video. They will make a new X Men Pro video soon for sure. Not sure if they will do a video for the TRON code update.

I have sent a email to STERN asking about TRON code update because a purchase of that machine for me relies upon new code. I will let u knowe what they say !