The sequence 1-2-1 is inexorable regardless of the reference frame.
The lines O1 (blue) and O2 (green) correspond to the trajectory of the observers. The brown triangle represents the light cone and the small circles represent the signals from the detectors (events) when the light arrive to them.
For the O1 one of the detectors of O2 turns on first, later the both his turn on simultaneously and finally the other one of O2 turns on.
For the O2 one of the detectors of O1 turns on first, later the both his turn on simultaneously and finally the other one of O1 turns on.
In the graph 2 we see the drawing that makes the O2 where his timeline would be vertical and the line of O1 would be inclined.
In conclusion, both observers watch the same sequence 1-2-1 of events. This sequence is inexorable.
For more information see the video: Length Contraction and Space-Time animation.
Elvis Sibilia of America