Not directly relevant but is "Dag" a male or female name? Can it be used by both?
Cleaning up "surnames" around Dag "the Wise", King of Uppsala but noticed that his mother is also named Dag.
Could be slight confusion by new user or inexperienced researcher or just me :)
The MP version of Dag Dyggvasson is here:
Dag "the Wise", King of Uppsala
His mother is an NN - the saga source doesn't mention her. Likely the entry of Dag as her name was an user error.