I'm from Argentina and a lawyer.
The form Surname1 Y Surname2 with the Y (and) between the two surnames is a usual way in the 'declaratorias de herederos' in the inheritances procedures to denote paternal and maternal surnames of the heirs.
Rarely it's used for naming people in real life as was used in Spain in the XIXth centuury.
The double surnames in revision list of russian ruled territories are quite usual (I have two cases in my family) and denote that the family first took a surname and then take another, so the record with both surnames intended to preserve the data for the future draft of the family's sons.
Also I see two surnames with the partcicle uel or vel that came from Latin and is like and in English.
Sometimes the double surnames in vital records are there because the mother was present in the moment of the record but not the father, so the clerk quoted the paternal surname between brackets.
KYLIN KILIM FRAJMOWICZ FROJMOWICZ TURNER ZARECKI MANOWICZ NEMIROVSKY ZAJDMAN CHAIT PORTNOY PUMPIANSKY KAPLAN CHERKASSY CHUDNOVSKY DAJCZMAN