The extension of the deadline just means that instead of cutting you off directly and you losing your sim and credit they now give you six months to (re) register it, they will reinstate the sim and your credit, but could take up to 24 hours to do.
I did mine again recently despite giving my PP details when I bought the phone, I had to sign a form and show my passport again.
My misses registered on line and was cut off, I went in this morning, showed my PP and signed the forms for her phone, so it looks like if you don`t sign a recent form then you get cut off.

FACUA has a bit on this. It says that the government will allow the mobile to be reconnected but it does not say until when you can do this.
https://www.facua.org/es/noticia.php?Id=4593


I cannot find this on FACUA website but it also seems they have made a "denuncia" against all mobile phone companies as they cut consumers off even if they have money on the PAYG SIM card. As I understand it you have to add money after so many months (each company is different) or the number is cut off. Here is alink from our local newspaper about it.
http://www.lavozdegalicia.es/dinero/...9540372503.htm
So even if you have registered you could still be cut off. Then you seemly loose your money.

24 hours ?...... 5 days and still waiting. ;-((