Hi @RobCGutshall,
Thanks for the extra info. This is going to be a really tough one to provide much help with, unfortunately, as systems and processes are so different and individualized to the school.
In general, I would agree that the former admin almost certainly did some kind of manual sis-import for the user enrollments. The big question I'd have is whether they documented that process at all so you could repeat it. The canvas-side of this is pretty easy (go to admin- -> sis_import and choose the properly-formatted CSV file(s)). The complexity is in getting the data needed for those files and then generating them. Instructure does provide the specs for the CSV files so you can see what will be required. It's most likely that you'll need a users.csv (this creates the user accounts) and an enrollments csv which adds the users to their courses. If there is no documentation from the prior admin, it might require some sleuthing to figure out what values were used for things like the sis_id of courses and users so you can maintain consistency.
I honestly don't know how much Instructure usually helps with this kind of thing... I think it's usually up to the institution to do this part, but perhaps Instructure does help out some. We've had this automated through scripts that run on a regular basis for the last 11 years, which is highly beneficial. If you can get to that point eventually it would be great, but I know the first and most needed step is getting things up and running for this year. If you have specific questions that we in the community might be able to help out with, please do let us know!
-Chris