Yes, you are right - I'm not from Autodesk.

As about your question about predefined paper sizes - maybe it is a good idea, but printing system on Mac is completely different from PC and AutoCAD can use one of the printers (plotters) installed in Mac OS, than you get paper sizes from this printer. The other paper sizes you need to add manually.

BTW, it you create custom paper size from within AutoCAD and pick on "+" button:

you can choose from the list of predefined paper sizes prepared by Autodesk.

You will agree - the list is imposing

Maxim