I'm not arguing, as there is no argument to be had. GMH intended the HX-HZ Sandman to be seen as a separate model so it is. HQ-HJ never really were, they were just extra goodies like a Thunder. HX-HZ were upgraded into a different vehicle from their base.

FYI Monaro used a Kingswood's model codes. Monaro LS used a Premier's model codes. Monaro GTS had its own codes but Monaro GTS sedan used a Kingswood's model code for HQ. Monaro LE used a HX GTS's model code. GTS sedan in HZ used the same model code as HJ-HX Monaro GTS and the same as LE. SL/E Statesman used Caprice's model code. XU1 used a GTR's model code. ALL of these are intended to be separate models. It is how it was done, end of story. The only reason a GTS327 was given a different model code from GTS in HK (and subsequently in HT-HQ) was to hide the HK from US scrutiny as GM had a worldwide ban on racing, it was originally intended to be a GTS with L34 engine option, and the first car built was exactly that - a Warwick Yellow GTS with L34 engine option. GM performance cars in the US were all done as option packs on lesser models. This is how Z28, ZL1 etc were all done.