Just a silly bnny trying it's best

So, okay. In the Anime, Nurse Joy is one of a couple of NPC families, probably an in-joke about being based on an RPG. In the original series, they were all identical individuals who were related (through marriage inexplicably sometimes) who shared the same name.

Not only are they physically identical, but they also have regional variants, which honestly are just like clothing style and hairstyle differences as art changes aside, they still look similar enough between regions that a hairstyle change could make them pretty good ringers for one another.

But, then in Diamond Pearl, they delivered this shocker:

We met Marnie and Page Joy and their father, Karsten. The implication is that

1.) Nurse Joy genes are passed down matrilineally. Anybody can have a child with the Nurse Joy and there is a chance they'll be like a clone of the mother.

2.) Joy is in fact their last name and that too, is passed down matrilineally. Having a living father does not stop them from having the last name Joy.

Now, Horizons/Pokemon SV gives us a unique specimen. A teenage/young adult delinquent Nurse Joy. Now, the Mossui Town Pokemon Center Lady isn't CONFIRMED to be a Nurse Joy relative and as far as we know, there's no other nurses in her region that resemble her.

In the most recent Japanese episode, we also see a Grandma Joy, confirming in fact that Nurse Joy does age, but also she's a Kanto Nurse Joy with a unique hairstyle compared to even the Joys at the same Pokemon Center.

But, then there's Molly. Molly is the first Pokemon Nurse who's a main character. She's IMPLIED to be a Nurse Joy as she claims to come from a family of Pokemon Doctors and is seen eventually working for Pokemon Centers.

When she as a young Pokemon Doctor, she bore a passing resemblance to a Galarian Nurse Joy, but notably, has always had a distinct design from the identical Nurse Joy family, which grew more distinct when she became independent and decided to travel the world treating Pokemon rather than stay at a Pokemon Center.

Finally catching up to the subs and Gramma Joy is in fact Mollie's mother. Both her and Mollie are 100% confirmed to be specifically Johto Nurse Joys, despite Mollie's distinct rebellious fashion sense.

Outside of Mollie tho, we do see this one Nurse Joy off duty sporting a completely different look in her civvies in Kalos, suggesting against previous evidence that the Nurse Joy look is more a uniform than anything else.

BUT, ALSO! You've got Pesselle from Pokemon Legends: Arceus, suggested by the text to be the Ur-Joy, the ancestor of all modern Pokemon Center Ladies.

So, okay. The Joy of Pokemon, an episode in the Orange Islands introduces an invidual Nurse Joy specimen of a Brown Nurse Joy (who also has super-strength, but that's not relevant actually).

They also flash back to her youth and show her roughly the same color, which means she ether has always had a fierce tan since she was like 6 or that's just her skin color. She's also always worn a lil' Nurse hat and is always shaped like that, Marnie and Page style.

Oddly enough, we see her whole family and they're as pale as regular Nurse Joys. Her sister is even confirmed to be the Nurse Joy in the Banned Episode "The Ice Cave!" in Johto.

So like tan or recessive genes or what have you.

Now we've also got Archaeologist from the Orange Islands and Pokemon Gym Inspector Joys who still just look like that regardless of their job (the archaeologist has a little nurse cross on her hat and is referred to as Nurse so she might be moonlighting) unlike the Kalos Nurse Joy, they don't change appearance when they're out of uniform.

We also got Nurse Joy M.D. PHD who also sports a degree in therapy from Celadon University, but who wears a stylish Neru collar shirt and black miniskirt, making her look more like an actual doctor than a cartoon nurse, save the hat. She also is the only Joy I'm aware of to need glasses.