Say I have these 3 usergroups:

1. GENERAL: access to most -- but not all -- forums.
2. SPECIAL: access to same forums as GENERAL, plus the SPECIAL forums
3. EXTRA-SPECIAL: access to same forums as GENERAL and SPECIAL, plus the EXTRA-SPECIAL forums

I do not want members of the GENERAL usergroup to be able to register for any other usergroup, and I don't want SPECIAL to be able to register for EXTRA-SPECIAL. I could be wrong, but it looks like this is a registration form where anyone can choose any usergroup they want.  

I can certainly see the value of users being able to choose their own groups, but our situation is such that we need to limit access to some of our forums to only people who paid to attend an art instruction webinar we are presenting. It's so they can share their progress with other attendees and the instructor without the worry of "outsiders" giving non-constructive criticism.

An add-on that would let me import a list of email addresses into a PRIVATE usergroup and then allow those users to somehow complete the registration would be great. If the email address already exists in the forum db, the import should add the Usergroup to that user's profile and not change anything else.

I'd be first in line for an add-on like that! And I don't think I'd be alone, either.   

Thanks again!

Let try using Secondary Usergroups.

1. Edit the two new usergroups and check/enable the option "Can be used as Secondary".

2. Then buy wpForo User Custom Fields addon, add new field in the registration form "Choose your Community" . So the user could select one from those two usergroups and automatically get according secondary usergroup on registration. The secondary usergroup will let them access to according forum. Here is an example of the addon usage on Registration Form: https://addons.wpforo.com/community/?foro=signup

https://wpforo.com/wp-content/uploads/2020/06/wpForo-custom-fields-on-registration-page.png

Please navigate to the Dashboard > Forums > Members admin page, check the users you want, then in the "Change usergroup to…" select box selects the usergroup you want and click on the "Change" button. See the screenshot below:

I am aware of this, but the problem is that, as per my OP, I expect a large number of users whose qualifications need to be verified before I can allow them in. Sometimes the email address is enough... but often it isn't (they may be using a different email for my verification records than in the forum).  If I have to research, it would either take forever or just be unbearably tedious. 

If I could isolate the list by a specific registration date range (not last login), it would at least mean fewer names to sort through. That would be an interim option, but it doesn't appear to be an option.  

What would be better is if I could send some sort of a forum access link to a list of pre-qualified name (emails) that I want to invite. They click the link to go to a specific form, then either register OR log in. The link would then add them to the usergroup I specify when I set up the link in Wpforo. If it had to be another paid add-on, it would be welcome one! Is there a feature-request forum I'm overlooking?

I can create many usergroups, but there are only 5 user roles and I can only sync one usergroup per role. If I cannot sync them, what is the advantage of usergroups over roles? It seems the only thing I can do with them, in effect, is rename roles.  Or does it matter whether I sync them or not, why/why not, when does/doesn't it matter, etc.

The WordPress User Roles like subscriber, contributes, author, editor, etc don't have any affection in forum accesses. They are not used in forum. They are synched with forum Usergroups. And forum Usergroups are used to get different accesses to different forums.  In the forum, there are no Roles like Subscriber or so. wpForo has Usergroups for this purpose. And each Usergroup is synched with WP User Roles. For example Subscribers are the same users with Registered Usergroup. The Registered Usergroup is the same Subscriber User Role. You can see that they are synched together in Forums > Usergroups admin page. So saying Subscriber Role you should understand Registered Usergroup in wpForo Forum.

I also didn't find the answer I needed most: if there's an easier way to add masses of members to a usergroup. From all appearances, it can only be done manually. As I said, I was able to control access to specific forums to specific usergroups, which is exactly what I wanted, but if I can't add members to those usergroups relatively easily, it won't do me any good.

Please navigate to the Dashboard > Forums > Members admin page, check the users you want, then in the "Change usergroup to…" select box selects the usergroup you want and click on the "Change" button. See the screenshot below:

I can create many usergroups, but there are only 5 user roles and I can only sync one usergroup per role. If I cannot sync them, what is the advantage of usergroups over roles? It seems the only thing I can do with them, in effect, is rename roles.  Or does it matter whether I sync them or not, why/why not, when does/doesn't it matter, etc.

I also didn't find the answer I needed most: if there's an easier way to add masses of members to a usergroup. From all appearances, it can only be done manually. As I said, I was able to control access to specific forums to specific usergroups, which is exactly what I wanted, but if I can't add members to those usergroups relatively easily, it won't do me any good.

I apologize for my ignorance but I would greatly appreciate more information than what I was able to find.

Please follow this support topic, to better understand the wpForo Usergroups, Forum Accesses, and WordPress User Roles: https://wpforo.com/community/faq/wordpress-user-roles-wpforo-usergroups-and-forum-accesses/

Also, I assigned both of them to the Subscriber role, but this interferes with syncing (if that even matters -- I have no idea).

To complicate things further, Community 1 should be accessible to Usergroup A only but Community 2 should be accessible to both Usergroups A and B. 

I would like to be able to do something like, for example, to invite them (by email) to register in a way that they automatically go into the correct usergroups (maybe a URL link?).  Or maybe import them to those usergroups with preset usernames and allow them complete registration as they wish. 

Or is there a better way of controlling access in this situation? This is the first forum I set up and I am clueless about all this.