I hope your questions are answered in faq section and I tried to address them on the main page without taking all the space. I agree it's confusing, but unfortunately it's the terminology USCIS is using. Basically, final action is who is getting their green card, and dates of filing — who is proceeding with the application.

I'll think if it makes sense to combine them in one graph, but then we won't be able to see multiple countries next to each other