Mini was its own marque by the end of the 60’s, though, and I think the only time they were “officially” imported to the US was after that.
I think the only problem with that explanation is why would they feel the need to change the code? It’s not like they were selling them simultaneously or anything. Car marques change ownership all the time. I presume a brand-new Jeep has the same code as an old Kaiser or Willys era Jeep.