One of my top five knitting books of all time is Knitting in the Nordic Tradition by Vibeke Lind. Elizabeth Zimmermann reviewed it by saying, "One is strongly tempted to call this all-embracing book the ultimate in historic Northern knitting." It really is that good and although long out-of-print, you can still occasionally find inexpensive copies via Bookfinder .
This pair of men's Selbu gloves was done using a pattern from the book. You can see the dark spots at the base of the fingers where I added rows to make the fingers more anatomical. Not so attractive but they fit DH very well.
The book has several pages discussing thumb gussets and she calls thumb gussets which start on the back of the hand "Norwegian gussets" as opposed to the sore thumb gussets which stick straight out of the side of the hand. What really intrigues me though is this diagram of an unusual crooked thumb gusset - it only has increases on the inside of the hand. I definitely have to try that one out in my glove research.