Ollisaarinen
Thank you. I already get the information that years 1928, 1929 and 1930 include overwritten coins. These overwritten coins have been made from 1 markka coins 1921-1924 (5 g 24 mm as you mentioned).
Thulium, a member of world of coins, our new partner, is Swedish, if I remember correctly. Join WOC and you can communicate directly with him per PM.
Take care
Ole
Globetrotter
Coin varieties in French:
https://monnaiesetvarietes.numista.com