You guys can't understand when people are just joking.
Everybody knew the premise was gonna be just shattered, it does says so too in the description, but that still does not deny the fact that the original intention of Yamada was getting 100 friends with benefits. It did not imply she would succeed nor fail, and timeskips are an easy plot device to employ. Actually, ep 6 will already be 2nd year if I remember the preview properly, which means a whole school year passed by in 5 eps.
The title is a joke too... can be read and interpreted in a couple ways at least, but your interpretation, post-it, is a really absurd one with no real ground to base it on. "B Gata" can be interpreted both as "B type" (as in blood) or "B cup," whereas "H kei" can stand both for "H style," "H group," or "H person," with the H clearly standing for "ecchi" in all of them.
In any case, the original plan would want the plain Kosuda to be a smooth transition for Yamada, who is still virgin, to get more experienced and therefor feel more secure when going to bed with the 100 sex friends. It just so happens that she really is that inexperienced and she actually ends up falling in love with Kosuda.
In any case, Ish's predictions on the end are both good imho, although my personal guess is that she'll wind up having sex with Kosuda later than sooner (yes I mean it like that) after realizing that she wants it for love and not just for pleasure, and she'll just stick with him or something.
