If Frank Kaplan was divorced than they may have married outside of NY, perhaps NJ.
My husband's grandfather was divorced in NYC in 1913. The divorce papers specified that his ex-wife could re-marry, but he could not. Two weeks after the divorce he got married in Paterson, NJ.
An index to NYC (or maybe just Manhattan??) divorces is at:
OLD RECORDS & ARCHIVAL MATERIAL
Division of Old Records