TCAS Fan quotes...
ANO Article 43, to "reasonably satisfy himself before the aircraft takes off.....that the flight can safely be made, taking into account the latest information available.....".
So I would suggest therefore a non-radio
equipped aircraft encountering a "pop-up" TRA would have a reasonable defence providing the pilot could prove (s)he had departed before the restriction came into force...
What does a TRA really provide though... a guarantee of protection? Not really, only a possible chance to prosecute any infringement after the event.