Penexchange

I´ve got a Pelikan 520 NN.
I´ve been told that it´s from 1957-1963 but another person tells me that 520 NN has been reproduced in the 90´s.
How can I see if I´ve got an older version or a new?

I have a pelikan 520NN. It is in good shape.
It has an engravement on the cap "Mauritz Gunnarsson".
How much can this pen be worth?
Is it a rare pen?
Is there some information about this edition?
/ Johan in Sweden