1980 Norwex 80 - Stamps from 1980 M/S

1980 "Norwex 80" Min. sheet values on 4 illustrated covers each with special exhibition cancels:
1. 17/6/80 "OLYMPISKE LEKERS DAG"
2. 16/06/80 "POSTHISTORISK DAG"
3. 20/06/80 "POLARFILATELIENS DAG"
4. 13/06/80 "APNINGSDAG"