Iwachu square cast iron nabeshiki (trivet)

Something tells me that this cast iron trivet was made by Iwachu, but I am having trouble putting my finger on exactly why I have that feeling.... Oh I guess it could be because it says so in big letters on the back. A very well documented piece that bears what I call the old Showa (1926-1989) mark, a Kotobuki label showing that company carried Iwachu cast iron decades ago and a rough "JAPAN" mark showing it was probably not made for export, but possibly marked after manufacture for Kotobuki Trading Company of San Francisco, CA. It is small, 4.25" square, weighing in at 10.1 ounces and with a couple of bends in the top. This style of trivet was popular a few decades ago, but I think it is still made by Iwachu. This ones has a teapot ring on the top showing it was much used. I need to do some research and determine exactly when this mark was in use but having trouble finding good sources.