No 'Tips and Notes' past Demonstratives skill
None of the skills after the Demonstratives and Defining skills in the Polish tree have any grammar notes. Is this a mistake?
Other courses came into beta with their notes done. I'm not faulting the Polish team, I'm just saying that just because it's in Beta doesn't mean it can't have completed notes.
Yes, it's a mistake. They should fix it, but Polish course is in beta, so there might be some mistakes.
There are plenty of resources on the Internet for Cases. My advice is to create essentially your own "Cheat Sheet" documenting the endings for each case and have it handy to reference. I found that being forced to create my own Cheat Sheet helped me a lot and that over time I have to use it less and less. Eventually the notes will be there, but that's the price of wanting to be ahead of the crowd. ;)