What happens to my handicap after an exceptionally good score?

If your Score Differential is 7.0 or more strokes better than the Handicap Index you played off, an extra reduction is applied automatically:

• The reduction is applied to each of your most recent 20 Score Differentials (or all of them if you have fewer than 20), so it stays in effect and fades as new scores come in.
• Reductions for more than one exceptional score add up.
• Your Handicap Committee is told, and can override the adjustment if it wouldn't fairly reflect your ability.

Source: Rules of Handicapping (2024), Rule 5.9.