I honestly don't know much. I just shared the link because it mentions the date being extended to the 15th of January. I've bought a phone into the country myself two weeks ago and forgot to have it registered at the kiosk in the airport. Later on I heard the date has been moved ahead so I just have to make a call from my phone and it will be automatically registered.
When I enter my phone's IMEI on the PTA website it says my device will be automatically registered AFTER the 15th of Jan on the condition that I insert a sim and make a call or sms before the aforementioned date.
As for people bringing a phone into the country after the 15th, I think it is manditory for them to have registered at the airport. And in case they forget to do so, I believe they have to visit their local customs office for registration. Atleast that is what I've heard man. I hope that helps