the relatives account of what Sarah Stanton may have said, is that Oswald had a coke in his hand (or "pepsi") at the time of meeting, so either Oswald had already gotten a Dr.Pepper from the 1st floor machine by the rear stairs or he had just gotten a coke from the 2nd floor lunchroom machine and exited the lunchroom BEFORE Sarah then saw Oswald.
In either case, that would be before Oswald is seen sitting in the 2nd floor lunchroom by Carolyn Arnold at 12:15 depending which FBI statement or which later 1978 statement by Carolyn Arnold is the correct one.
So if Oswald already has coke or Dr.Pepper and he is on his way down to eat lunch in the Domino room, that would have to be in the range of about 12:10 to have seen Norman and Jarman at that time, still in the TSBD. They left sometime very shortly after 12:10 and not later than 12:15 to go around to the front of the TSBD.
So what did Oswald do then? Did he stay in the Domino room from 12:12 until about 12:14 and then went BACK up to the 2nd floor lunchroom, got himself ANOTHER coke, and then he decided to sit down there and continue eating the remainder of his lunch there for at least another few minutes such to be observed by Carolyn Arnold from 12:15?
If what Oswald is alleged to have stated in Will Fritz office is that he "went out to see the presidential parade" then it follows that Oswald must have left the 2nd floor lunchroom a few minutes after 12:15 to go down to the 1st floor lobby, and perhaps that is why there is also the Carolyn Arnold FBI statement of having seen Oswald on the ground floor at about 12:25.
But getting Oswald out the door and standing somewhere on the front entrance and then back into the lobby again and either meeting Baker there on 1st floor or on the 2nd floor lunchroom later is a very difficult problem to work out especially with no witness at all having seen Oswald after 12:25 until about 12:31:30