relation back

noun

re·​la·​tion back

: the assigning of a prior date (as the date of execution of a document) to an act (as filing of a document and especially a pleading) as the time of its effect especially to avoid a time limit

the relation back of amendments to the date of the original pleading

also : the legal fiction that an action (as the filing of a document) was taken on a previous date to avoid the expiration of a time limit