CREATE TABLE table_61874 ("Colliery" TEXT, "Location" TEXT, "Date" TEXT, "Year" FLOAT, "Death toll" FLOAT, "cause" TEXT)

When has a cause of gas explosion, a Death toll smaller than 63, and a Location of penygraig?
SELECT "Date" FROM table_61874 WHERE "cause" = 'gas explosion' AND "Death toll" < '63' AND "Location" = 'penygraig'
SELECT "Date" FROM "table_61874" WHERE "Death toll" < '63' AND "Location" = 'penygraig' AND "cause" = 'gas explosion'