Exactly!
This is the cord I have today. Amazingly I got 2 large folders of paperwork with this RV with things like the previous owner's insurance docs, registration renewals and of course the pile of appliance owners manuals that you get with an RV, and nowhere does it mention if the rig is 50a or 30a.
I actually converted our previous Terry TT from hardwired to a 30a Marinco shore cord setup, so I was familiar with that part, but I had never seen a 50-30a adapter cord like this. Live and learn and appreciate comments from folks here!