You are correct ... for Moodle. The chart was taken from roadmap for Joomla and their LTS schedule.
What I was trying to suggest ... and failed ... was this .... best, I think, to setup a such system as OP is proposing where both Joomla and Moodle are running LTS versions. Hopefully, make it easier to update both without breaking the key plugins for interfacing Joomla and Moodle.
Joomla, on the admin side now, has updating core checks built into it. You login to the admin side and if there is a update/upgrade, you are notified with a nice button to click and perform. It even has another checker for extensions (in Moodle-ese, plugins) that one can configure by pointing to a URL to acquire updates for those plugins as well. Admin of the Joomla can add URL's to the plugin checks. One is there if admin has installed JCE (a veru good editor - not part of core Joomla) ... installation of that also installs a URL for checking for updates to the JCE. Hopefully, joomoodle or which ever Op is using, has setup such a place to update their plugin - in Joomla as well as in Moodle.
Went over to the joomoodle site (hope I got the right one) and checked their forums ... appears they were having issues when 3.0 was released ... they fixed with a patch at first and then made an update available. It seems to me, that should not have happened ... if they are creating and plan to maintain plugins/etc. that do what it does, when Moodle has a new release they would test and head off any issues customers might experience from the get go.
When this sort of plugin/additional feature affects logins/authentications, a broken anything on either Moodle or the Joomla means down ... no access ... and for a site selling courses, some students who are upset cause they can't get to a course for which they plunked down some cash.
Also very import the admin of such a system be able to get to either/or/both directly with an admin account that uses local (to Joomla, or to Moodle) authentication to be able to get to the backend of both. There's potential for breakage IF op uses CSV in Moodle to globally set accounts ... ALL accounts ... including the one that should always remain manual ... that of the initial admin account.
I see 'E' and Op are gonna get together privately and work on whatever Op wants to do. That's good! Op is getting help Op needs. So if nothing else, I've muddied the water enough to get someone a 'gig'! ... which if fine.
'spirit of sharing', Ken