Let's take anonymous access for a minute.
If you have anonymous enabled on Confluence and Jira Software (onPrem) you can allow anonymous users the ability to read the content with linking from one to the other all hunky dory.
The minute you force them to log in to JSD as a customer although they can read the knowledge base attached to the JSD project, they can't read any Jira software linked issues on the KB. When they come out of JSD they can't read any of Confluence as they are now logged in and don't have a license.
There must be a way to use the three products together and only buy the required amount of licenses for each of those products who need to be able to create content surely?