Short explanation: Them changes hide in the third decimal.
Now take a glass of milk and a seat ;)
Preliminaries:
- With your history, I assume that your average is saturated. This means some guesswork is involved because we don't know all of your best 500 Legend scores.
- Just gross scores count towards the average, no matter on which course.
These 9 hole scores doubled, you played a 60 and a 62.
The story:
In a saturated average, a new score may kick out a higher one (if available) to provoke a change. As a guess, there may be some 64 scores in the mix. Now a 60 enhances the scores' sum by 4. Divide by 500 = 0.008. You may not see this change if the average was 62.144 before because 62.136 is rounded to 62.14 again.
Next score, a 62, makes up for 2/500 change in the average. That's 0.004 only, but don't be surprised to see the new 62.132 average as 62.13.
End of story.
Side remarks:
- I'm quite sure to have hit your true "highest score" because
(65-60)/500=0.01 would have been visible at once. The story would work
with 63, too, but not with 62 => impossible with an average above 62. no change from the second game.
- it works similar in an unsaturated average of a high number of rounds, except for being linear, no "kick out".
- lowest possible change is 1/500 = 0.002. Four of them may hide in rounding.
(edited)