I have had a look at the "Road Route Numbers" dataset myself and it appears to just be R1; whereas South Road between Richmond Road and James Congdon Drive, for example, is designated R1 and A2 (I struggle to think of another such case). The corresponding signs also state both.

Interestingly, I noticed that they've got Victoria Road (to Outer Harbor) designated A16 in that dataset, despite the corresponding signs stating A9.