My question is, how long have you played a game incorrectly without realising?

Either due to software issues (like previous owner changing a bunch of settings that drastically changed the game)
or
Mechanical things not working, or being incorrect parts.

For example
2 weeks ago I finally realised that a machine I have owned for 1 year and 2 months had the wrong part installed. I had never played someone elses machine before was it wasn't obvious to me

It was my Seawitch, and it had a 1 way normal gate instead of the flappy orbit guide it was meant to have
It wasn't obvious to me since all most footage and pictures are straight down. I always thought that the game was just designed bad and had average geometry
I installed the proper part yesterday and cannot believe how much of a difference it makes to the gameplay. 14 WASTED MONTHS!

Can anyone top that?

Ha! My lotr came from a top tournament player so he had all the settings on extra hard and it took me a couple of weeks to realise. The reverse to your situation I couldn't start any multiballs.

Hard to tell with whitestar as there is no default settings shown like Sam and wpc games

When I got family guy earlier this year the right orbit Spinner was hitting the top of the bracket. So it wouldnt spin more than half a turn before getting stuck.

The guy that sold to me said the game was boring. Turns out he never got into a mode once and it was on almost base code. Bought and sold the game without knowing you need to rip Spinner to start a mode