Can someone tell me why I can’t see my neighbors second floor joist ? (even though I can see my neighbors second floor ceiling joists )

Here are pictures and more background 
https://drive.google.com/drive/folders/1-1Nyw95ejVjZEyCmNogZ_Z7XsY9xIcpM

1 house is 2 story wood frame 
2 house has continuous stud from foundation sill to second floor ceiling 
3 house was built in 1920
4 party wall appears to be 4 inch wood stud , with brick infill 
5 there appear to be horizontal bridging in the party wall at the second floor framing . The bridging could  be 2 double plates
6 . I do not see a ledger (ribbon ) at the second floor
7 there is a possibility the second floor joist are cut like a 90 degree birds mouth to sit on a double plate 2×4 that is running along the length of the party wall

still It’s a mystery why I can’t see my neighbors second floor joist (I do see my neighbors second floor ceiling joists )

8 could the original builder have lined up my joist and my neighbors joist in the same plane so each of us have only 2 inch bearing ?