the calendar date in which your account posted to the IRS master file.
The first six numbers are the cycle week and the last two numbers correspond with the day of the week.
Cycle Code Ending in 01= Friday
Cycle Code Ending in 02= Monday
Cycle Code Ending in 03= Tuesday
Cycle Code Ending in 04= Wednesday
Cycle Code Ending in 05= Thursday
so the 7th week in 2021 on Thursday - 2/18/2021