I agree: they had a plan B, which was, at some stage, consolidated into the specific Jack Ruby deception.
One detail I forgot yesterday with regard to the images of (apparently) the real Ruby at the press briefing: in both films he is in the corner of the room (in his WC testimony he said that he was 'standing on an abutment'): in one film you get him for only a few frames at the start of the film (although they usually pan slowly across a still frame first - the Rheinstein Effect) before the actual film starts and the camera moves away from him - and in the second film you see him (but only half of his face) for a split second right at the end of the film. Both of these look suspicious because of the brevity of Jack's appearance. (see attached for reference)
In the former film he is not wearing his glasses, but he has them on in the latter film.
I'm not sure whether Ruby himself moves in the former film or whether it's a still image brazenly pasted on. I'll have to magnify and slow it down enormously. The head of another person (below Ruby in the image) does move, and that distracts the attention almost every time. It reminds me of that story Robert Morningstar tells about blinking at the same moment in the Zapruder film twice.
The 'Corridor Ruby' who walks out behind Wade is not wearing glasses, and in the corridor footage he seems to have the white handkerchief in his breast pocket but no glasses (as seen in the Beers and Jackson photos).
I have attached the color still of Ruby in glasses from the movie again, just to mention the fact that I think that they wanted to emphasize it.
I was surprised to see that Linda Zambanini stated online (I can't recall where) that the Corridor Ruby figure was 'not Jack Ruby'. I sometimes wonder whether these people have a 100% grasp of their own assassination cover story.
note handkerchief circled
Notice partial view of Ruby above on the right, wearing glasses.
So, could they have pasted that image of Ruby in?