One needs to check whether all of the families declaring their descent from Piotr Wlast do really come from the same male ancestor.

One also needs to check whether the Rajecki and the Rajewski families are related by blood.

If so, this would be fruitful to discover whether those families are related by blood with another European families, and escpecially those which clame their descent from either Ragnar Lodbrok of Sweden, or Erik I Ejegod of Denmark.