Thanks for your message.
That does sound about right. There was another version of CJT PLUS 1.1.2 before it jumped to CJT 8.4
We wanted to provide a similar versioning structure for Free/Core and PLUS to keep things synchronised and make it less confusing. So as things currently stand, the CJT Free/Core version on WordPress.org is at 8.4.1 and the latest CJT PLUS is at version 8.4
It is interesting why it is saying that the update is unavailable for this plugin though. Can you send an email with temporary admin credentials so I can check your license section.
Sorry for the confusion.