That date is when Apple addressed the defect, and started producing earbuds that weren’t affected by static or crackling.
So, if I heard static or crackling when using my AirPods Pro, I’d probably tinker with the earbuds right away.
Apple started a service program to fix affected AirPods Pro in October 2020, allowing users two years past the date of purchase to fix their earbuds.
When you take your AirPods Pro into Apple, they’ll take a look at both the left and right earbuds and will then replace whichever unit is affected (or both if the whole thing is shot)?