Here is a possible way to reconcile both Carolyn Arnold sightings of 12:15 in the lunchroom and the 12:25 sighing of Oswald in the lobby, with the Fritz notes of Oswald referencing Norman and Jarman
and the more recent find of the "outside to watch the P. Parade" note
and taking into consideration Eddie Piper sighting at 12:00 and Oswald possibly having told Piper "Im going out"
and Oswald NOT seen by anyone between 12:01 and 12:14 on the 1st floor, even though Norman was still in the Domino room at 12:00- 12:10, and Jarman was wandering around on the 1st floor eating a sandwich from 12:00 to 12:10 approx. After which, both Norman and Jarman exit about 12:10 by the back loading dock door, and arrive at the front TSBD by 12:15
And Buell W. Frazier not having seen Oswald with a lunch size paper bag (unless Oswald put a lunch bag inside the longer 24-27" bag Frazer)
The sequence is therefore:
Oswald comes down to 1st floor at 12:00, meets Piper, and the reason to even say anything at all to Piper, was because Oswald was going to leave the building to go "Out" in order to buy some lunch. Thus Oswald was letting Piper know, so that Mr. Truly would know not to waste his time looking for Oswald inside the building or sending someone to find Oswald.
Just before Oswald returns to the TSBD, probably via back door loading dock, Norman and Jarman leave via that door about 12:10 and go around the outside perimeter. Its possible Oswald could have had LOS to them at this point in time, as they go around the corner, past the Domino room.
Oswald returns into TSBD via back door at about 12:12, stops by the Dr. Pepper machined on the 1st floor by the back staircase, gets the bottle of pop, and goes up to 2nd floor to see if its empty of the office women yet. As he reaches the 2nd floor landing, he sees Sarah Stanton, and Stanton see him. Oswald sees also possibly, a few other women still in the lunchroom so pretends he is just on his way up to another floor. Sarah sees Oswald with the Dr.Pepper in hand, which she may have told a relative some years later, and the relative remembered it as "Pepsi"
Oswald goes up about halfway the next staircase and just sits there,on the midlevel 3rd floor stair waiting and listening, hoping the rest of women will leave and the 2nd floor lunchroom will be vacated. He is out of line of sight here .
About 12:15, Oswald goes back down a half flight of stairs from 3rd floor mid landing where he had been sitting, and he sees that the 2nd floor lunchroom is now vacated. He goes in and sits down. Possibly he may have taken off his jacket and or his brown shirt here too.
Carolyn Arnold then comes to get some water and sees Oswald sitting in the 2nd floor lunchroom approximately 12:15. She then leaves, probably returning to the front staircase, using the outer hallway, where she joins up with Virgie Rachley in the front Lobby by about 12:17 and by 12:20 they are standing near Mrs Reid and Mr. Campbell on the curb of Elm st.
About 12:22, there is radio transmission on one of the motorcycles near Norman and Jarman announcing the JFK motorcade is about to arrive in Dealey Plaza. Norman and Jamans thus depart to return to TSBD, going back around the side and to the rear loadking dock, returning thru the back door, and then to get on the rear West elevator approximately by 12:23
At 12:23, Oswald is still in the 2nd floor lunchroom. He has not quite yet finished his Dr.Pepper, but has finished his lunch. He decides he will go down "to see the P.Parade out front" .
Oswald exits the 2nd floor lunchroom about 12:23:15 and just misses seeing Norman/Jarman on the West elevator going up. However, he does HEAR them talking on the elevator.
Oswald then goes down, to the 1st floor, using the rear staircase, and across the floor, passing by Trulys office and into the front lobby, where he stops to the right side of the glass door entrance, and looks out thru the right side glass partition. This is about 12:25pm
Carolyn Arnold looks back towards the TSBD entrance and sees Oswald inside the Lobby at this time of 12:25, Oswald being visible thru the glass partition.
Now What? Does Oswald go out? Does Oswald stay inside the lobby and witnesses the JFK motorcade going past, hears the shots, then goes where? Back up to the 2nd floor lunchroom? Or to the first floor Storage room beside the front staircase?