It still looks like there is a problem with your contention that a rocket is a closed system. I suppose that you can define your own systems anyway you want, but you can see where it could cause some confusion when you deviate from the scientific norms at use by most scientists and engineers. When I consult my university thermodynamics textbook, I do find that there can be NO matter transfer in or out of a CLOSED system. Obviously, a rocket has a very massive exhaust as the majority of a large rocket’s mass is fuel and when the fuel is mostly burned the majority of the initial rocket’s mass has left the system. Of course, you could include the rocket’s plumb as part of the system boundaries but then those boundaries would have to be continuously expanding over time.
It's also interesting that you consider a human to be an OPEN system. That definition would be agreeable to most. Obviously, a human takes in mass in the form of food and water and ejects the waste mass that the body doesn’t use into a toilet somewhere. That's pretty simular to a rocket that must be fueled before departure (something that is also contrary to a closed system) and then ejects most of the fuel's mass to generate thrust.
https://en.wikipedia.org/wiki/Closed_systemThe information in the link agrees with my text books so you can count on it being accurate. Please be more specific, if you can, regarding your unique definition of a CLOSED system and specify its boundaries.