Hello Dale,
With all due respect to Vashavsky, he collates information that has been published in various books, on websites and information given on items purchased, and he does a very good job of it, but a citable source it is not, and there is no information on how the material attribution was reached. I am happy to share a single example, but this is part of active research I am conducting and when I am I ready to release the full results I will. I am not here to convince you or anyone else of anything, I just have knowledge in the area and thought it was worth mentioning. Below is a classic Kagami-shi Tsuba, I actually have two in this style, likely from the same workshop and you can see a similar example published in the Sasano's Kagamishi Tsuba book.
The composition is:
Copper 83%
Tin 12.88%
Iron 0.88%
Silver 0.37%
The remaining being made of trace elements of various things.