When is a Magpie Black or White-backed?

Received yesterday The Australian Bird Guide. Pre-ordered from CSIRO. Only
3 weeks after the local bookshop had it in and we live in inner Sydney. So
I’m a bit late to the book review party

Anyway to get used to how the guide worked I looked up a very common local
bird. Well one I could see out the window – Australian magpie and
immediately got very confused. The guide says there are 8 ssp but only
mentions one in the text – the western form dorsalis. The images have a
random selection of 4 of them but no mention of distribution (except
terrareginae which I assume is Queensland).

Back with the text the authors decide to lump the unnamed ssp into 3
groups, namely black-backed, white-backed and western. The text for the
white-backed reads “(3 ssp) occurring e and s of Great Divide from se Qld
through Vic to Eyre Pen” and the distribution map reflects this.

Surely this is wrong. Here in Sydney I thought we had the nominate race
tibicen which I know from my own travels and observations seems most
definitely black-backed and is distributed down the east coast from
Queensland to just north of Eden where white backed takes over.

The Guide however seems pretty convinced that white-backed now covers the
east coast from Vic to Qld. So am I missing something in all the lumping
and splitting and have I just got to accept that white is now the new black?

Cheers
Chris Gregory