HSV products had to be approved by Holden as they did in the HDT days with Brock and were the only corporation Holden formally recognised to enhance their vehicles, hence HSV components are listed in Holden's parts books, Walkinshaw components aren't. Kicking around somewhere, I've got a VL (Walkinshaw) parts book supplement printed by Holden when their parts books were hard copy. In later times, I think non HSV Holden dealers were locked out of parts listings for HSV VIN vehicles only HSV dealers could access. There was a time you had to provide an HSV VIN# to order HSV parts and if some dealers suspected you were abusing the system, they'd refuse to order parts.