As you say, you restart frequently, meaning that a large number of your “total plays” never make it to the full 3 balls, so by dividing by 3 you are artificially compressing the partial games of only a single ball into fewer total plays, which is of course not what you’ve been doing. The logic for counting total plays is, in all likelihood, just the number of times start has been used without regard to whether all three balls in the game actually get played or not in the end.

I could be wrong, but I think lifetime plays is just what it says. The total plays, total balls, etc. get reset to zero when you reset audits. The lifetime count does not.

As for how many full games you played, that can't really be answered. You have two equations with three unknowns, so there are lots of possibilities. If a is the number of 3-balls games, b is 2-ball games and c is 1-ball games, then:
a + b + c = 1070
3a + 2b + c = 1702

Now, if you always play either all 3 balls or quit after ball 1, then you had 316 full games and 754 1-ball games.

I'm usually a "restarter" too. I go through phases where I try to play all games straight through, but they don't last. I noted the same problem as OP when trying to determine how many games I've played. On modern Sterns, I found a way to get # games played.

There are audits that give number of games played per a time range. This data seems to be generated only by COMPLETE games. For instance, at one time I noted that the sum of these "timed" games was 1637 games, compared to 3426 "total plays", which I assume includes the restarts.

I was calculating average game time, and dumped audits and imported to a spreadsheet, screenshot copied below. This might give you an idea as to how to determine total complete games (just ignore right 4 columns).

beatles spreadsheet (resized).png

Audits menus -> dump

and on my machines it asks you to insert a USB drive. There are USB jacks in the back box (can't remember which one works). Machine will dump text file to USB drive.

IMG_7106 (resized).jpg

Either USB port should work. Whether it's for audit dumps or game code updates.

Can anyone confirm which was the first Stern pinball machine to feature lifetime plays in its audits menu? (that couldn’t be reset with a code update)
I always thought it was Iron Maiden; Legacy of the beast

99% sure my xmen pro had it, but then it skipped couple years and came back.

So this feature was started in 2019 so Munsters was the first to have it initially. However then any game that received a code update in 2019 would get it. For instance my DP and GB got updated then they received it but it is not "true lifetime plays" Its lifetime post 2018. I do see alot of ppl trying to pass off there GB and all those previous games as having that low number tho so be careful anything made before 19 as the correct odometer reading cuz they could've put thousands of plays on GB cuz it was out 3 and a half years before that update in September of 2019.