Wikipedia, and similar community-driven websites, is not a credible resource. By dictionary definition, it is "a woman who is married to one's father after the divorce of one's parents or the death of one's mother". To keep things communally correct (i.e. within the majority community of couples who have sought out/used genetic donations), I'm using a) community-preferred terminology, b) what is scientifically correct, and c) what is legally correct—in that order.
Thus far, there is no legitimate source confirming Pennsylvania acknowledges illegitimate children as stepchildren. I've found something on foreign affairs regarding marriages and stepchildren, but it's directed at immigration standards. If you can back up the relationship with at least three credible sources, we can discuss changing this with the rest of the Finding Carter Wiki users—even a legal doc and one article would suffice.
The definition of stepchildren also varies throughout the world, hence why a legal confirmation is needed, or even some articles proving it. This guideline was set in place after discussing with several peoples in similar situations (my cousin is a surrogate for a same-sex couple, and she runs a popular mommy blog I occasionally post on, so I used her connections/access into the community) what the preferred terminology is, for the most part.
The Wiki needed a standard guideline for many relationships, because too many people couldn't agree on one thing, and edit wars are exhausting. In some ways, this standard/argument is similar to the one about Elizabeth not being the twins' biological mom, even though she actually—and scientifically/medically—is.
I hope this makes sense. :s
Edit: Forgot to add this: