Derivation
variable: stillmardate (table[s]: all_spouse_pairs_full [derived table])
variable: rmardate (table[s]: all_spouse_pairs_full [derived table])
variable: rsepdate (table[s]: all_spouse_pairs_full [derived table])
The earliest date either couple report being married to this partner is used first (i.e. the interview date when the partnership first reported when they are married to them). It is updated to the earliest co-residency date if this is earlier. After all the dates have been finalised this date is removed if mardate is available.