CREATE TABLE table_204_77 (id DECIMAL, "number" TEXT, "builder" TEXT, "type" TEXT, "date" TEXT, "works number" DECIMAL, "notes" TEXT)

how many different types of diesel locomotives are dated after 1980 ?
SELECT COUNT("number") FROM table_204_77 WHERE "date" > 1980
SELECT COUNT("number") FROM "table_204_77" WHERE "date" > 1980