A recent article about how aging paint affect the color items in portraits really emphasizes this well. The image in the left is the portrait as it is today and to the right is how they believe it looked before it aged. (Photo is from a a story in Whim magazine that can be found here: http://www.ruwhim.com/?p=46076 .)
One of the key things to consider, when working to recreate a look from the past is that every few years you might need to evaluate what you know, or what you think you knew. Yes, this means it will be entirely possible that you might need to rework areas of costumes you have already spent countless hours on. Yes, this means that papers you have written or that classes you have taught might need to have edits done.
Honestly, I think this is part of the fun of what I do. It keeps things alive, dynamic. New discoveries or new light on old discoveries keeps me motivated and allows me to explore and try new things.
It looks like 2016 could be a year of interesting new information for those exploring Viking costume and I am very much looking forward to it. A book on the Gokstad textiles is due out this year. And two books that cover costuming are already available for pre-order.
Textilien und Tracht in Haithabu und Schleswig. Die Ausgrabungen in Haithabu 18 is already available from Amazon in Germany. http://www.amazon.de/gp/product/3529014184?psc=1&redirect=true&ref_=od_aui_detailpages00
And Iconic Costumes: Scandinavian Late Iron Age Costume Iconography is available for pre-order via Oxbow books: http://www.oxbowbooks.com/oxbow/iconic-costumes.html
(I have to add in here the caveat that I still personally avoid the Shoulda/Coulda/Woulda approach to reenacting. Yes, what we know is forever changing, but I base my work on what we do know now, and not what we might, possibly, find in the future.)