CREATE TABLE table_203_717 (id DECIMAL, "number" DECIMAL, "year built" DECIMAL, "livery" TEXT, "current status" TEXT, "notes" TEXT)

are the most trains operational or do they have another status listed ?
SELECT "current status" FROM table_203_717 GROUP BY "current status" ORDER BY COUNT(*) DESC LIMIT 1
SELECT "current status" FROM "table_203_717" GROUP BY "current status" ORDER BY COUNT(*) DESC NULLS LAST LIMIT 1