It seems that I can stack accessories with Henchmen after they are trained.  Basically, I will design units with four accessories, and when they're trained those Accessories show up on their profile picture but not on their equipment list (but the values are there). I can then visit a store and purchase those same Accessories again and put them on and increase stats. Those new accessories (even if the same exact ones) will show up in their inventory and can be worn, also showing up on their profile, including duplicates.