Know issues are always fixed in new versions, especially device support. The old 4.1 gives black screen in normal not supported devices.
It is theoretically not possible to support all devices and even some new devices in motion tracking, even by Google or Apple, while some devices are missing sensors sometimes for some reasons.
We changed the behavior to give on screen text and more logs (there should be logs in the old versions too but easily ignored by many developers) for such cases since some versions after, so you will not have a pure black screen anymore, and you need to give proper actions to those devices.
So, do not use the version before 6 years. If you want to know if an issues exist in that version and fixed after, just run the latest sample and see what happens.
For migration, read
https://www.easyar.com/doc/en/develop/unity/migration/guide.html
API to API migration guide is given in that page for version 4001 and later. For versions before 4000, a high level guide is offered and it is not that easy while sometimes internal APIs are marked public and used unintentionally.
BTW, the whole EasyAR documentation has been re-written and it is strongly suggested to read it first, it is totally not the document you see before two months.