Hi David,
The top two on your Traffic Screen are Commercial (CAT) ADSB - denoted by the 'A' in the 'Mode' column. They are reported as being 72 and 80 Km away so should have been inside your tablet's visible area, but both being above 38,000 ft, would only have appeared if you had 'Show Vertical Separation' in your tablet software set to something like +/- 40,000ft or more (which you could do for test purposes, but which would be crazy for practical flying).
You are right about the mode 'C' entries - the T= ? in the Sq(uawk) column denotes time that each entry (in this case Alt(itude) ONLY) has been held in the system for processing. 'Bearingless' Mode 'C' and Mode 'S' targets will ONLY appear on screen if selected in 'PilotAware/Configure/ Mode C/S Select' and only when the Sig(nal Strength) of the received signal breaks one of a set of predetermined trigger values, set by selection in the 'Mode C/S Detect' 'Range' section on the PilotAware configuration page.
As Keith says, this will all become clear if you read the PilotAware Operation Manual, but please feel free to come back with anything you still don't understand.
Regards
Peter
(Development Tester)