The only place I can think of where you can find that information is the “Enrollment” tab of each individual ILT course. There you can filter by “Without session enrollment assigned” under the session options if you want. Unfortunately, this tab has no “Export as...” function like other tabs when you select (all) users. So I assume if you want to have that info for a specific course only, this would be the best way to get it. 

At least I’m not aware of a specific report that shows that data. But I’ll follow to see if someone else has an idea.

Unfortunately I haven’t seen this information available on a report.  You can filter on the Course Management page down to only ILT courses and then “ILT Sessions Options: Without Session enrollment assigned.” to see a list of courses that are impacted, but you can’t export the information.

The only work around I can think of to see this in a report format would be to run a Users - Courses report with all your ILT courses or the ones you know are impacted, then run a Users - ILT Sessions report on the same courses.  If you splice the reports, you should be able to find the “outliers” that show on your Users-Courses reports, but are absent from your Users - ILT Sessions report.  It’s not exactly elegant, but it might work for your purposes.

Yeah, you’re not crazy. the in UI method is typically best for most people as you can track. You can do this via the API as well, and is a simple enough one you don’t need any tools or know how to use the API really, detailed this out here in case you are interested: