subdate
/ˈsʌbdeɪt/ or /ˈsʌbdˌeɪt/Definitions
1. verb
to date or assign a date to (something) as a subsidiary or subordinate of a main date.
“The historian subdated the historical events in the new timeline.”
2. verb
to move or be moved to a position subordinate to a main date or position.
“The new employee will subdate to the assistant manager position after six months.”