Yep, just not all the ones that are know, or at least named. For example we know that the first 'Mechs produced by Nova Cat, Ghost Bear and Sea Fox/Diamond Shark are the Vision Quest, Minsk, and Fox respectively. And the first ASF produced by the Cats and Sharks are the Quasit and Ogotai. And at some point during the Golden Century the Vipers cranked out the Storm Giant 'Mech.
Six designs do not quite an XTRO make unfortunately. :-\