I really don't know how it works, it's yet another reason why Miiverse was so much better. Back in Splatoon 1, you could still see your own post in-game in one of the designated spots that the post shows up, if it's done by the drawing feature that is. But still, actually 100% knowing your post made it through is really what made it great. And the best part is, popularity wasn't part of the equation of it at all, avoiding the problem of seeing posts from the same exact people every single time.