CREATE TABLE table_203_607 (id DECIMAL, "catalogue number" TEXT, "artist" TEXT, "release title" TEXT, "format" TEXT, "release date" TEXT)

which artists had more then 6 release titles
SELECT "artist" FROM table_203_607 GROUP BY "artist" HAVING COUNT("release title") > 6
SELECT "artist" FROM "table_203_607" GROUP BY "artist" HAVING COUNT("release title") > 6