I also agree that there’s more around than what that formula would render but maybe not a huge percentage more.
Here’s 3 of my machines using that formula.
1970 Flip a Card: 1800 made.
2020 left: 56 machines
1975 Wizard!: 10,000 made
2020 left: 470 machines (approx.)
1962 3 Coins: 1100 made
2020 left: 20 machines (approx)
I think there’s definitely more out there in most all cases. I could see those numbers being: 90, 1000 and 45 respectively. Just a guess