The biggest issue to Not Forgotten is Kimura outright. Her scenes create complicated issues as her pure hatred towards X-23 drives her to some pretty violent extremes that go above and beyond torture. She literally cuts X-23's arm off with a chainsaw towards the beginning of the story. That alone would guarantee an R rating. Leaving it in though creates some pretty bad ass scenes where we get to see Laura cut loose without any restraint whatsoever. X-23 takes out every operative, security personal, or otherwise scientific asshole in the place that wants to use or abuse her to create more like herself. She does this literally single-handedly. It shows outright just how X-23 cannot be stopped when she puts her mind to something by outright showing she can do it even with one arm tied behind her back. Err, well incinerated with someone else hanging onto those claws for her for later re-implantation.
She uses triggerscent in the sprinkler system to roar unbiased against all the torment she's faced and even manages to incapacitate Kimura in a quite beautiful metaphorical way by literally shutting the door on her.
It's an epic story outright. Poetry in motion fully with how it's written and presented. Violent, gritty, and yet also just unbridled passionate bad assery that shows that a woman that hits her breaking point will not be stopped by anyone to do what she feels is right, even saving those she can along the way as Laura makes sure that Agent Morales is secure before starting her unbridled onslaught against the Facility.
It's pure carnage done by one lone woman with only one arm.
Definitely R rating material.
So how do you adapt that while still keeping the soul intact but trying to lower it to PG-13? Can you even?
Even by lowering it from the chainsaw to just torture, you're presented with the issue of X-23's unabashed pure rage against them for everything they've taken from her. It's a bloody action packed story no matter how you look at it.
So if you remove the entire chainsaw incident from early on, now you're left with X-23 that has two arms and still ready to tear everyone in the complex a new one.
Not exactly something that'd lend itself to less than an R rating either.
Would it matter though? We're talking about a story that's so eye-widening that it'd make even the Matrix fill up the old man diapers it's wearing by now. So it begs the question. Should X-Force even bother with trying to maintain a PG-13 rating? Or should it just go for the gold, and present the story with all the awe-inspiring visuals it can to showcase exactly why you do not screw with these people and their families? Should it just go straight to the R rating for showing exactly how one woman can be the scariest woman on the planet and exactly why you do not corner her?
Here's a video digested version of the story by lauraXx23 from Youtube. Now imagine that expanded to 90 minutes or 120 minutes with the rest of the team handling a different mission that keeps them occupied from rescuing Laura right away. I don't know about you, but I'd probably never leave the theater because I'd be re-watching it over and over and over and screaming encore every time the credits rolled.