You need to escape the inner quotation marks.
"date -d \"$1 $2, 2019 $3\" +%s"
So turn it into
'{d=system("date -d \"$1 $2, 2019 $3\" +%s"); if ( 1562731201 < d ); print}'
You need to escape the inner quotation marks.
"date -d \"$1 $2, 2019 $3\" +%s"
So turn it into
'{d=system("date -d \"$1 $2, 2019 $3\" +%s"); if ( 1562731201 < d ); print}'