My point mostly is if these 1063 users should all be in the Registered user group as their primary group, shouldn't all of your other users also be in the same Registered group as their primary group, and other groups just applied via secondary groups? How many other user groups do you actually use as primary groups? Looking at your list of user groups, you only have Administrative, Events and Moderating. If some of the other users have these groups as their primary group, and the Batch Update Users method I mentioned above affects them too, this might not actually be a bad thing. The general recommendation is that everyone should have the base set of permissions set via the primary Registered group, and any additional permissions cumulatively added using secondary groups.
So, another approach is this:
Search for all users who are in the Events primary group, change the primary group to Registered and add "Events" as a secondary group.
Repeat for Moderating and Administrative if applicable.
Then the only users remaining should be the others which presumably should just only have a single user group, which is "Registered" as their primary group.
I'm not actually sure there would be a way to properly refresh any permission caches, so the method above is going to be a lot safer.