CREATE TABLE table_204_816 (id NUMBER, "locomotive" CLOB, "named" CLOB, "serial no" CLOB, "entered service" CLOB, "gauge" CLOB, "livery" CLOB)

what locomotive is just previous to bl29 ?
SELECT "locomotive" FROM table_204_816 WHERE id = (SELECT id FROM table_204_816 WHERE "locomotive" = 'bl29') - 1
SELECT "locomotive" FROM "table_204_816" WHERE "id" = (SELECT "id" FROM "table_204_816" WHERE "locomotive" = 'bl29') - 1