Hi David and Tim.
I had a look at the reports and report sources and can see what's going on. The certification embedded report pages are designed to only show the data for the user who is viewing it, which is why you can't see a full list of users with certifications when you view it. However, if you create a custom report based on the report source then the restriction to the current user is removed. Unfortunately, it seems there was some confusion during development as to whether the report sources would be used this way, so the user fields weren't added (although "Record of Learning: Previous Certifications" does in fact have the user fields and they are commented out in "Record of Learning: Certifications" source, very odd). The user fields should be in most (or maybe all) of the "Record of Learning" reports, but one of our devs will have to investigate to see which ones are applicable.
I'll put a bug report in to get someone to fix this. I'm not sure if the people higher up will consider this a bug or an enhancement, so I'm not sure how it will be prioritized. Until then, David, you can try creating a custom "Record of Learning: Previous Certifications" report and see if it contains enough information for you.
You could try removing the "//" disabling lines 156 and 365 of totara/plan/rb_sources/rb_source_dp_certification.php and try creating a custom "Record of Learning: Certifications" report. If you do change the code, please be careful as it needs proper testing to ensure that it doesn't introduce any other problems (it seemed to be ok from my quick test).
Tim, you might want to try making the suggested change and seeing if the custom report sources will then be equivalent to what you were planning to do. If you're planning to build something beyond that then we'd be keen to see what you've done and consider if it can be integrated into core Totara, but you'll have to talk to someone higher up about how that would happen.
Any other questions please feel free to ask.
Nathan