Hextech Chest Question

Hey Summoners! I just needed some quick help. I just played a Normal Draft Pick game with a party of 5, and I was confused because I didn't get a chest at the end... Basically, yesterday I got an S- on Ashe so I got a Hextech Chest from earning that score. Then today, I just played this Normal Draft Pick game and my friend and I BOTH got a S- during that game. Unfortunately, I didn't get a chest from myself because I had obviously already gotten one on Ashe the previous day, however I didn't get a chest from my friend who was playing Kassadin. Is there a reason for this? Because I do know that it is possible to earn chests if someone in your party does get a S victory... but I didn't. Could it be that since I already earned an S on Ashe I can't earn ANY chests from myself or anyone as long as I'm playing her? I tried looking this up but nothing game up.

Thanks for the responses and help, BrawlicSnake