I was going through some old keys, and found one of the "Adams Rite" original Commander keys. It was my impression that all Commanders used that key when new (along with a similar baggage door key, which I also have one of). When I flew for Aero Air in the 1980s, every pilot was given a door and baggage key, for general use.
I also heard that it was a "Boeing" key, which would open any Boeing airliner cockpit door of that era.
I imagine most Commanders have moved on to different door lock systems (mine certainly has), and I'm pretty sure Boeing no longer uses the one key system...