Jira Software Server, REST API, JRJC version compatibilities

[emacdonald]

I'm tasked with writing a piece of software that will pull data from Jira Software Server versions 8.5 and 7.13. I plan on doing so with the REST API, so my initial task is to determine which versions of which APIs to use to do so.

When I go here: https://developer.atlassian.com/server/ and click on "REST API" under JIRA Server platform, I am taken here: https://docs.atlassian.com/software/jira/docs/api/REST/8.9.1/.

However, v8.9.1 isn't the version I want to support, so I click on "List of all Jira REST APIs", and am presented with a list of OVER TWO THOUSAND VERSIONS, none of which are 8.5 or 7.13! And, the same page that provides a link to over 2000 versions of REST APIs also boldly claims "The current API version is 2."

So, my first question is, how many versions of the JIRA Server REST API are there? And if your answer is 2 (or any number less than 2000, for that matter) -- what are these? https://docs.atlassian.com/software/jira/docs/api/REST/

My second question is, what versions of the Jira REST API do the each of the five major releases of this project: https://bitbucket.org/atlassian/jira-rest-java-client/src/master/ correspond to?

I'd really like to use JRJC so that I don't have to re-invent the wheel with respect to serializing and deserializing Java and JSON objects, but I can't seem to figure out which version of it I should be using.

thank you!