Hopefully, someone will point me in the right direction:
1) Calibre 2.4.7, running under Win10, cannot see the single book downloaded from Kindle Store. The Nexus 9 is recognised...
2) Calibre Library books appear to be loaded into N-9 main memory but Kindle reader cannot see them and neither can Aldiko. Aldiko cannot find the Kindle book either.
A Nexus 7 running the same version of Android and Kindle App reads all books without any problems whether they come from Kindle Store or Calibre Library.
What am I missing, please?