Because Mrs Reid has made a very early FBI statement of having seen Oswald in the 2nd floor office very soon AFTER shots fired, then it became imperative to establish a timeline to make sure Baker was seeing Oswald BEFORE Mrs Reid, otherwise there might be a potential plausible alibi for Oswald .
there was probably effort made to avoid contradictions between Baker and Reid.
If Oswald drank some portion of the coke during Bakers encounter, then it might be questioned why Reid would have seen the bottle as full.
Plus, the theory is that Oswald has just run down 4 flights staircases in haste to escape TSBD, so drinking a coke already in hand just 5 secs after “diverting just in time to avoid running into Baker and Truly “ might raise a question.
So easy fix: strike out “drinking a coke”
What about the “light brown jacket” which was definitely in contrast to Reid seeing Oswald in only a T-shirt?
Baker could “fix” his early light brown jacket description as who would believe he could mistake a white T-shirt as light brown jacket?
The best fix they could do was to have Baker in WC testimony explain how he mistook the Oswald long sleeve brown shirt as a jacket.
They left the issue of T-shirt Oswald to the speculation for the public hopingfor the “Oswald must have taken off his brown shirt just after Baker left the lunchroom”
And The Story becomes Oswald must bought a coke AFTER now that Baker, and Truly 2 now, In WC statement disavow seeing a coke.
So the Mrs Reid sort has been preserved as best they could do and Belin has done his stopwatch timeline to fix the story and everyone is satisfied now.
Except about 75% of the public which Hoover and LBJ were trying to convince that there was no conspiracy.