I'm posting this in case anyone else has this question...

For multi-page surveys:

LastPage blank means participant loaded the first page, and did nothing from there (either have just started the survey or abandoned it without clicking Next).

LastPage = 0 means participant clicked Next, but didn't answer all the mandatory questions, and either abandoned the survey, or they are still working on the first page.

LastPage = -1 means they clicked back from the first page to the welcome page, and abandoned the survey.

LastPage > 0 is the question, or question group page they last completed.

Good summary. Unfortunately, forum posts might get deleted or disappear. Ideally you would include this into the manual.

You see I wrote the same on June 19th.
But nobody will come across that thread anymore.

So it really is the best to include this in the manual.

Joffm