I'm not quite sure what you mean but, back when it was possible to complete the list (and I have the achievement for doing so) it was only possible if you were not Lauren's BF (so not, presumably on a "lauren playthrough") as, while you could have sex with Lauren as her BF (thus crossing off that part of the list) you could not make out with Autumn if you were Lauren's BF.wait what? I always thought the list part was primarily intended for a lauren playthrough - the Autumn part is a change if anything; I remember being surprised that she would swoop in on her sister like that, but I think that used to be enabled.
In other words it's not Lauren that changed, you always had to be close to her, that was normal. It's Autumn's mechanical forks changed :/
It was possible to have a kissed status with Lauren (basically have made out with her a couple of times but not triggered BF status (eg don't have sex in Paris), I think I've posted how to do that previously) and get her to have sex with you after the party (at which point you became FWB) but this was, apparently, playing the game wrong (Not enough CONSEQUENCES! or something) and has so been memoryholed.
Now you just can't have sex with Lauren unless you're already her BF which makes it impossible to complete the list.