That math in the bottom half is correct. That is how .500 works.
If you are 10-10 and you win a game, you are 11-10. That is half a game over .500, because .500 would be 21 points and you have 22.
If you then go to be 12-10, you are 1 game above .500, because potential .500 22 games into the season is 22 points, and you have 24.
I get where you're trying to go with this but I just don't see any real logic behind this way of thinking. Say you are 10-6. By my definition you arie 2 wins over .500 because .500 16 games into the season is 8 wins, and you have 10. By yours, you are 4 games over .500, because if you remove those wins, your team is .500. The problem I see with that is if you remove those wins, that .500 number is the .500 stat for 4 games ago. That does not show what the potential .500 is for the current amount of games played, but rather shows an older version.
You have to stay current when doing it. If you are 10-6, .500 at that many games played is 8-8. You have to compare your standings to what .500 currently is in order for it to work.