...no problem. [posting after successfully arriving airside]

It helps if you know your HKID number, but even if you don't have that it should still be okay, might just take a few minutes longer. Immigration staff do some searching on the computer, verify you are indeed a HKID/PR holder, might pull you aside for a moment, but no more than a few minutes of inconvenience. Very friendly staff in my experience.

To clarify, I have now encountered this problem both as a HKID holder (I was on a work visa, before 7 years when I obtained PR), and now as a HK PR.