by Ken Task.
Are users in the 1.9 backups? One can find out by unzipping the backup.zip file on a local computer. One should see a users.xml file.
If users were in the 1.9 backups and 2.4 did not pick them up, one might have to resort to using the users.xml file for a front page backup from the 1.9, and 'scrubbing' that file to create a users.csv file. One could then bulk upload the users.csv file. That can be done - have.
Some work to be done still ... enroll users to courses and assign Teachers to courses - etc.
The only way to 'get it all' is to do a site migration but that *might* require some expertise beyond most mere mortals to pull it off - that's the impression from some posting seen.
'spirit of sharing', Ken