@Background Pony #2E21  
That’s unfortunate.

Soon this will have to be updated, as it’s been revealed that Fluttershy has a brother.
 
And like with these two, that’s probably all we’ll know before he appears in the show.

@The Twelfth Doctor Whoof  
I don’t see a problem with Shining not being mentioned. My college friends don’t know thag I have a little brother, whom I am very close too, and I don’t know if several of them have siblings either. It’s just not a subject that gets brought up without it being relevant to a current topic/situation.
 
We know that Twilight met with her brother several times during season one and two, which means that we only missed them because they were off screen.

@EyeGuy  
There were only two sisters, but Maud is older than Pinkie, and her not being on the farm isn’t a stretch at all.
 
They couldn’t have used either of Pinkie’s sisters in the plot of the episode without changing their personality; both siaters were shown dancing at Pinkie’s party, which would go against the whole entirely emotionless thing.

@EyeGuy  
This is true.

At least there’s nothing completely CONTRADICTING Shining’s existence in the first two seasons, and it’s entirely possible Twilight and Spike talked about him offscreen.
 
In Season 1, we saw a flashback to Pinkie’s family. There were plainly and clearly only TWO sisters.
 
Plus, at least Shining’s existence introduces interesting new plot points. With Maud, there was NO reason to give Pinkie a third sister. They could’ve used one of Pinkie’s two remaining sisters, and it wouldn’t have affected the story.

And they both turned out to be pretty good characters.

@The Twelfth Doctor Whoof  
I’m going to laugh if the animators edit her into the Cutie Mark Chronicles.

One difference, already mentioned: Maud got some foreshadowing in-show via that photo in “Pinkie Pride” (even though she didn’t appear in “Cutie Mark Chronicles”; that can be explained away by any number of plausible reasons, like simply being late to the party).
 
Shining Armor got zero advance notice at all, which would’ve been fine if Twilight hadn’t described him as her B.B.B.F.F, which made no sense in the greater context of things.

What if Maud is actually Golden Laurel as an earth pony?

@Background Pony #2E21  
No, that’s because Scootaloo’s parents have careers and lives in Cloudsdale, and sent their flightless daughter to live with family friends in Ponyville so she wouldn’t fall off a cloud and die.
 
(Or she’s an orphan. Or she was outright disowned by her folks for flightlessness. Or they followed Cloudsdale tradition and set her out on a rock to let her die of exposure, but a kindly couple, or orphanage director, from Ponyville took her in. Or… … I like my headcanon better.)

They have something meta in common?  
Better ship these two.

This explains why we haven’t seen Scootaloo’s parents.

@Spiritus Arcane  
We at least saw her before we figured it out, that’s the point.

We didn’t know Sweetie was Rarity’s sister until her THIRD appearance, so quit making a big deal about relatives that don’t even live in town!

@EQUINE_excite  
Yeah, naturally. But not because of Shining Armor.

@PonyPon
 
Forewarning sure, but RCW is just fine.

My OC is the 4th Apple sibling who’s been there all along

@Roboshi  
Pinkie has two younger sisters, and yet do nothing with them.

At least Maud had a short forewarning and a relativity good episode behind her.

That’s why they like to keep families undefined for as long as possible.
 
For example, Rainbow could have a sister we don’t know about until they want to do an episode about her.