Well obviously a plan B didn’t happen, so how would anybody know?
Doesn’t Thomas Arthur Vallee in Chicago at least give you some pause?
How do you know Plan B didn't happen? Perhaps the murder of officer Tippit was part of it, as it seems to be of a more improvised nature than the assassination.
If there was a plot to kill the President, blaming some random dude for it must have been an integral part of it, like Milteer said.
Now, selecting Oswald as the patsy was a master stroke of genius, given his treacherous background, his Russian wife, his odd behaviour and lack of social skills etc. But in order to make it work Oswald has to show up for work, preferably carrying a long bulky package, and not be in the presence of others who can provide him with an alibi at the exact time of the shooting.
That's a shaky foundation for such an elaborate scheme. Therefore it seems logical and rational that a reserve patsy was on stand-by in the wings. Who was it?
I don't know who this Vallee guy was you mentioned, but I will look him up - I think he is mentioned in JFK and the Unspeakable.