I have got to say I don’t like using parts book description to determine if it can be removed. It may be unavoidable but it seems pretty arbitrary. If one company says that is a seat support and another says it is a bulkhead stiffener should that be the determining factor.
Some Miata guys are having to change their cages because on the optional forward foot protection bars they attach to a piece that the factory calls something other than firewall even though there installation are the same as what we do in IT.