The thing is, no one can define GNC, because how far do you take it?
Not all lesbians grew up with short hair, dms, shaved heads, doing spot welding. Some do. Some do it in response and intentional rebellion against the stereotypes being pushed on them that they don't related to. Others are fine with the dolls, the long hair, the feminine clothes and activities, and just like what they like. Yet the act of fancying other female people is in itself GNC.
The only real answer is that gender is a lot of constructed bullshit that cannot be pinned down, and female and male people come with a wonderful range of personalities, interests and preferences, which shift over time and in response to age, experience, culture, friendships etc. And it's bloody stupid for parents to panic and try to read something determinate into a child focusing on a toy that makes the parent feel uncomfortable. When really, this says everything about the parent's own psychological issues and nothing about the child and how they may grow up.
We will never know how people like Jackie and Jazz may have grown up if left to find their own way unsteered by adults with agenda and issues of their own.