In my "Collection -> Champions", I see that some champions have "Season's highest grade" A or less, but yet it says "Chest acquired". If I understood correctly, this means that a premade has scored S with that champion, so that I got a chest. (Is this correct?)
My question is: Can I still acquire a chest if I now get an S with one such champion?
And bonus question: do I always get a chest whenever a premade team mate achieves grade S-, even if "Chest already acquired"?