Unfortunately, before the mid-1900's, there was no official spelling for people and place names. Many of our ancestors were illiterate, and didn't know how to spell their names, nor did their parents. The spelling you got depended on who was doing the paperwork, and that could vary from place to place and day to day. People didn't think of spelling the way you or I do. If someone asked you, "What font do you use for your name?" you'd probably laugh and say, "I don't care, whatever font you want to use!" That seems to have been the attitude toward spelling names. Modern genealogists in Norway often spell the same person's name differently. So it's best to just pick one and stick with it.
A good description of all this is here at http://arvegods.blogspot.com/2012/02/norwegian-names.html
(Edited to add link)