@
FredFriendly
You seem to have confusedly used the term
retcon to describe what Coco-sensei used in this chapter and in a previous transgression. I'm gonna have to correct you here, for I am a fan of Warhammer 40k, and trust me when I tell you that
I know what true retcon is and the pain it brings. Bear with me cuz this is gonna be a long one.
Anyways, let's start by a simple description: a
retcon is a tool used when the author decides to change a previously established part pf the story, either to more properly fit his current vision, because it was a bad idea and the new one is much better or because he/she no longer likes it. In any case,
a retcon is something that can be told immediately, because it directly contradicts the past. There's also something called a
revision, which is when the author adds new element to a backstory in posterior work that doesn't contradict any previous information but still changes our comprehension of it.
What happened here and what you previously described were not retcons, but something else that comes rather close to it:
[ol]1)Chiyo and Yuna being classmates in high school not being mentioned at any previous moment in the story is not a retcon or even a revision, but a simple late information drop/withholding. It would have been a revision if it had been previously said that they knew each other from long ago and it was, at that moment, interpreted as them knowing each other from another moment other than highschool and it would have been a retcon if it had been stated that they met for the first time in college; the author simply never said anything about when they met and only mentioned it now with the flashback.
2)The eavesdrop is not a retcon either, but a simple case of the friend forgetting about it or simply not paying proper attention to it, she was too gaga over her prince to delve on Chiyo apparently knowing Ookuma from her past, not to mention that she doesn't know all the details
nor do we know what was it that she actually heard. It would have been a retcon if she had decided to not trust the guy or if it had, in any way, changed her perception of any of the two people; she simply buried it in a corner of her mind, had her vagina take over and invited the hunk for a date. In the worst of cases, the author just forgot about the eavesdrop and didn't let it affect the story, but still didn't retcon it.
3)As for the birthday changes... well, that
was a
retcon without a shadow of a doubt. I gotta give you kudos for actually remember such a small detail though, it would have simply gone past me hadn't you mentioned it.[/ol]
As for Igarashi... the poor guy is the buttmonkey #1 of this story, so get used to it; as long as there are no malicious intent behind the actions I say give them a bit of a leeway. They're not hiding it to harm him, make fun of him or to save their own hides, but because mentioning it would cause unnecessary drama and they don't think it's something that needs to be said at this point; them meeting this often is a matter of unfortunate events being played out for the sake of the story, in real life it's more likely that they wouldn't ever meet again after Igarashi gets a new job.