Stoneball... I believe there is an error with logic and not your math. In your examples A - B = C, you are spot on if everythng is in a perfectly straight line.
Since there are very few holes that are perfectly straight, and since there are very few golfers who can hit the perfectly straight drive down the perfectly straight fairway, there will be even fewer holes who's yardage adds like you think yours should.
When hit your tee shot, you are given the yardage your ball flies, in ANY DIRECTION. Where the ball comes to rest determines the yardage of the next shot.. from your ball's position to the flag IN A STRAIGHT LINE.
To test this get on the fairway with your second shot. If you have 100 yards to the pin, turn around and hit your 100 yard wedge BACK to the tee box. By your logic, you should be on the green, but in actuality, you're 200 yards from the stick.
Hope this helps. Have a nice day.