A version of the SBT remains standing. It is firm only if you ignore the evidence against it. And it is certainly challengeable.
The current version is not the version that the WC counsel were pushing, as the many references in the evidence to "first shot" being the one that struck JFK attest. John McCloy believed that JBC was struck by the first shot and did not feel it right away. It was not until many years later that the second shot SBT gained acceptance. So much for a "firm" theory.
The evidence against the second shot SBT is abundant: over 20 witnesses said that JFK reacted to the first shot - not by smiling and waving for 3 seconds
Few among the "20 witnesses" in your paper were actually in a position to see the President smiling. Of those, some (ie: the Chisms, Jean Newman) were "two shot" witnesses who merely recalled the President "slumping" on the shot which occurred before the head shot. That means their "first shot" was the second in most three-shot scenarios.
Mary Woodward saw the President not react (other than look around) to the first shot and "slump" on the second shot, followed by the head shot.
which is what the SBT requires.
It's "required" only to meet your arbitrary claim.
No one said he continued to smile and wave after the first shot.
But your list of 20 witnesses have few who were in a position to see the President wave clearly and even more who were not positioned to see his face.
There is abundant evidence (from motorcade witnesses, photographers, witnesses along Elm) that the first shot was between z186-202. There is evidence that JFK was visible to Oswald in the SN by z195 and likely visible all the time he was passing under the oak tree.
No evidence for the car clearing the oak tree by Z195 that you produced. Better-resolution film shows the branches were a considerable hindrance.
There is also abundant evidence that the shot pattern was 1.......2...3
Witnesses were more attentive to the shot span--if they were attentive to such a thing at all--only after hearing a second shot. They had no reason to expect a second loud report after hearing the first as many dismissed the first as a "backfire" or "firecracker". The first shot blended more readily into the normal behavior observed in the crowd and the motorcade. Only with the second shot came a wave of awareness and urgency.
so there could only have been one shot by z225 when the President is seen to be reacting. That in itself contradicts the second shot SBT.
As far as being challengeable, I am not sure what you mean. I challenge it. That does not mean that Oswald did not fire all three shots. He most certainly did.
Andrew Mason is a defense attorney and apparently will commit any lie, misrepresentation or distortion to "defend" his "client" (pet theory).