Law / Classic car registration in Poland [12]

Hi guys,

Would love some advice, I am about to buy an imported car (has been in Poland for some time already) but its not registered.

Is it odd that the seller has had the car for some time and not registered it?
What documents should I get from the seller.
Who should I contact to register it as a classic in Poland, its over 25 years old and out of production more than 15 years.

Anybody who has been down this road and who can help would be very much appreciated.

Paulski