At present, the old form of smart ID cards are still valid. The department will continue to closely monitor the progress of the replacement of new smart ID cards and has no plan to declare any ID card invalid at this stage.
You can just claim that you were not in Hong Kong. They literally never care. I know so many people who missed their dates.
The current HKID is still valid point - last official source here https://www.info.gov.hk/gia/general/...3022100608.htm
Also in the FAQ Qn 4 of the smartid immigration page.
I had to fill in and sign a form stating reason for not doing it per schedule - I wrote I misread the requirements and gave it to the officer. That was it..At present, the old form of smart identity cards are still valid. The ImmD will continue to closely monitor the progress of the replacement of new smart identity cards and has no plan to make arrangement for declaring any identity card invalid at this stage