Well, it can help if you're playing a champion you don't consistently get S's, but one of your (premade with you) teammates does.
Still, if you wanna double-check, go to your Profile, look at your Champions list, and hover over Shen. If he's got a golden chest, it would mean you've already gotten it while playing as him.
If you're especially obsessive and wanna triple-check everything possible (like me :P), count the number of Hextech Chests you've received and opened (excluding the free chest), then count each champion you've earned a chest playing.
As long as the number of chests adds up the same as the champions with an earned chest, then you're probably fine. :3