launch: Time(s) the start button on the experiment's start page was clicked. Note this does not mean the study was actually launched. Clicking the start button without having the player installed (as per the instructions on the start page) will do nothing.
license: time the player executed the license check. This, then, at least means the player was installed.
finish: time redirection to the specified finish page occurred.
> 1) What could be happening if someone has a finish timestamp but only 1 of the 2 data files?
Participant quit the study before one of the data files was created or an upload problem. Any not yet uploaded data files remain on the device and can be manually uploaded via the player's "Data" tab.
> 2) What could be happening if someone has a finish timestamp but no data files?
Quitting the study before there was any data, upload problem, or disabled automatic data file upload in the player (controls for that are on the "Data" tab in the player app).
> 3) Is it correct to assume that if someone only has a launch or license timestamp, they did not complete the study?
Typically yes, although there can be edge cases (e.g. internet connection went down while the participant was completing the scripts -- they do not require persistent internet connectivity), so redirection to the finish page may not have occurred or could not be logged.