Armor can be classified into 2 categories.
Kozane armor are the archaic ones, they mostly have the appearance of lacing and lamellar and little iron plates. Units that should be wearing this are either samurai who wield archaic weapons, like the Naginata, and the Yumi.
Tosei armor are the modern after-teppo-introduction ones, they range from the smooth ones to those with combinations of lamellar on the bottom and some other type, as long as there is no or sparse lacing. Units that should have this are either wield that wield Katana, Yari and teppo.
Now its not really historically happening, I can easily imagine a guy in Kozane and wielding a teppo but with this configuration mentioned above, it'll distinguish units much more easily.
Extra variation is good but when comparing with a Yari samurai with its full blown maedates all over the helmets and another naginata samurai having similar, it'll end up just the same. Between individuals there is variation but in between units, samurai end up looking all the same, a hodge podge of silver and gold maedates, archaic mixing with modern, modern breast plate with archaic shoulder guards. And the odd ashigaru wearing a modern "tub" armor
With this configuration of distinguishing archaic and "modern" you can easily made up who your units are. Lacing all over the place on Naginata, smooth and some other thing for the Yari.
Helmets are another
If it has a whole at the top with lacing, its archaic, if has none and the lacing space is far in between its "modern".