Hi Chris,
normally, I use a piece of flaking urushi. This is the best part i think. Or a piece of kawa kozane, but these can be older reused kozane. The lab gives an average timespan, withe a certainty of +-80%.
C14 is not 100% waterproof, but is is, as I said, to confirm my thoughts.
This dou is comparable withe the golden one of Maeda Toshiie. 1570-1580.
I tend to date armor on their style, proven reference material, and scientific examination. Not one of these 3 is an axioma, but the 3 together give a good impression of the reality.
btw, i c14 tested almost all my pre-momoyama armors. After 1640, these tests are useless due to sun fluctuations.
btw, the earlier Mori Takamasa's armor differs indeed qua muna ita and waki ita. i have to come back on my words, it may be later than 1580.