from what I read from You, ipdb (pictures and text) and looking into the schematics I say: To the different ways "Replay-Mode, Add-A-Ball-Mode is Extraball-Mode, Novelty-Play-Mode and true Add-A-Ball-Pins" - (A) I learned "Aerobatics" can be played (in Replay-Mode) making Replays and (one) EXTRA-Ball (called Bonus Ball) with a ball we are playing, having on the playfield - in play. (B) I learned "Aerobatics" may come as a true Add-A-Ball-Pin not having an Replay-Counter. (C) I learned "Aerobatics" Replay-Pin can be set / changed to true Add-A-Ball and still gives the chance to make one Extraball (called Bonus Ball) with a ball in play. This (C) way is new to me - we must check if this really is the truth.
Here https://www.ipdb.org/showpic.pl?id=24&picno=77594 we see on the bottom the 1 2 3 4 5 6 7 8 9 10 Game Over indicating "true Add-A-Ball, a new game starts on "Balls to Play 5" then as we play it slowly steps down to 4 then 3 ... . On the right of the ipdb-picture, a bit up we see text "Bonus Ball" - to me this is exactly the same as we are used to read "Same Player shoots Again (an Extraball)".
See here https://www.ipdb.org/showpic.pl?id=24&picno=67174 - the backbox of a (true) Add-A-Ball pin - NOT HAVING an Replay-Counter. Question: In Your pin - is there an Replay-Counter ?
When You change the plugging to Replay-Mode - Question: Can You make that "Bonus Ball" to light up ? and You get what we normally call an "Extraball" ?
Normal Extraball: We are playing a ball, make "Extraball" lighted - loose the ball - bonus is counted down, given - stuff on the playfield resets - ball is kicked over to the shooter-alley NOT stepping to next player / next ball - and I then play the Extraball.
callmedoor - please answer my two questions. It would be great when an owner of an Aerobatics-Pin would chime in and tell us about the logic in play.
Side note: The ipdb-schematics is a bit confusing - the mentioned "Extra Play Unit" is (to me) Replay Unit --- many strange wording and Argh - GAME-RELAY - I always have problems understanding an GAME-Relay. Greetings Rolf