@seasonsinthesky this doesn't really answer your question and some of the information I gathered came from the bowiestation.com site.
As far as I know the song Sue (Or In A Season Of The Crime) started during the Next Day sessions. Sue was then redone and appeared on the Nothing Has Changed compilation, Sue was then redone again and appeared on Blackstar.
These are some of the songs that are said to be left over from the Blackstar sessions,
- When Things Go Bad
- No Plan
- Killing A Little Time
- When I Met You
- Russian Black Man Of Moscow
- Somewhere
- Wistful
- Duet with Lorde (Bowie at least recorded his part)
- 5 demo songs from Dec 2015/Jan 2016
No Plan as well as Killing A Little Time and When I Met You, were released as Blackstar bonus tracks.
****Again these are not facts and are purely speculation based on hearsay, I can't even guarantee the source. The Bowie documentary The Last Five Years seems to back up some of this but again dates and recording sessions can not be verified. Tony Visconti in the documentary did mention that Bowie had demo'd five new tracks that they never got to work on before he died.****