Session Library differences between CI3 and CI4?

I don't know if it is fair to say "completely", but substantially rewritten is a fair statement.  That said, I think it fair to question the sentence "This detail was at the root of many issues and...". It fair to point out that's a quick rewrite of the copy from the v3 help. Whether it's true or not needs to be investigated.

Thank you for answering the question itself.
Thats what caught my attention first and put me on to this question. 
I am sure a good amount of time was spent to make the Library CI 4-worthy, but if it was not that to a point where it quacks like a brand new duck, then maybe that line should be removed (or as I previously suggested, make it a reference to the rewrite in CI 3) to avoid any potential confusion for others like me that likes to go through legacy docs.