Just as an illustration how it's possible to retcon anything if you think enough, here goes. In the vis.ret., I remarked that Sae could not possibly perform with Acchan, in good story terms, although we have canonical screencaps. But what if that's actually Sae the 9th in the screencap? I mean, okay, only Tomochins are virtually indistinguishable (and perhaps Mayuyus), but since we're bending the common sense, might as well postulate that Sae #9 graduated at a convenient moment, Youko was promoted to Sae #10, voila. She never admitted to working with Acchan, did she? We only have pictures, right? Thought so.