To actually give a serious answer (although from someone who was not part of the dev-team) there is generally a lot of freedom in Vikingr when it comes to several items. The Väslgarde helmet for the Norðmenn is a helmet of the Vendel Period (The period in Scandinavia before the Viking Age). Seaxes do appear in scandinavian context for the Viking Age, but there are only a few finds and the only one I know, which would be suit for combat, would be the one from Hedeby. (Which suggests that Seaxes in Viking Age Scandinavia went out of fashion.) The Coppergate helmet for the Engle is too early for the Viking Age aswell, the Yldrena Láf sword for the Wísa also has a design from the migration period. (So called Ring-Swords). You could make a whole list of things that are not 100% correct, but in all honestly, for the time it was made, Vikingr was still quite an accurate mod unlike other mods you had for Warband. And if the Devs wouldn't have taken that freedom, the item slots would probably be quite fewer than today.