CREATE TABLE table_68776 ("Name" TEXT, "Street Address" TEXT, "Years as tallest" TEXT, "Height ft / m" TEXT, "Floors" FLOAT)

During what years did the tallest building, located at 211 Union Street, have less than 31 floors?
SELECT "Years as tallest" FROM table_68776 WHERE "Floors" < '31' AND "Street Address" = '211 union street'
SELECT "Years as tallest" FROM "table_68776" WHERE "Floors" < '31' AND "Street Address" = '211 union street'