I never said that my friend was trying to recreate a history book correct look.

I said that he was living with what he has available and with what works.
They tried lighter weight fabrics and they were fine for show but when it came down to living, working, and keeping dry and warm they found the heavier weight and slightly fuzzy nap of the fabric to work the best.

To this group, who are all Anthropology and Archeology Professors, it is what works that is important. So they all know the books. Many of them can quote them from memory.

They use what the people of period would have had, and what they could have traded for. Saffron, for example, to dye their Leine was available and traded to the islands from southern Spain, but is literally worth its weight in Gold.
The Penannular Brooch is an heirloom. It's an actual one that has been passed down in the family.

Another example is their weaving of fabrics.
When weaving they don't always weave Tartan. Some times they weave Madras Plaids, sometimes stripes, sometimes Tweed. It depends on what and who they are weaving for and the mood of the weaver at the time.
Sometimes they weave lighter weight fabrics for summer and sometimes heavier weight ones for winter.

So these people, eventhough they know what is written in the books, and follow them as much as possible, find that not everything is in the book. Much of what is in the book is sometimes a strangers interpretation of what they saw, and sometimes was written long after the fact and sometimes was second or third hand verbal when it was finally written down.

So if it's cold and wet and snowy they grab what's warm and hang the description in the book. The idea is to find out what it takes to stay alive.