Probably not a very simple question, but I'm stumped.
Several years ago I came across (and saved) a QR code which, when scanned in one of the Alola games, produces a shiny Mega Diancie. As Diancie isn't in the Alola Pokedex, it obviously doesn't register it as a "seen" entry. However, it is not counted as a Wonder QR code - the game erroneously says that it's a Pokemon in the Alola dex, indicating that the game is somehow tricked into scanning a Diancie instead of whatever else the QR "should" be. I've attached the QR code as an image if people want to test this for themselves.
Legendary and mythical Pokemon don't have QR codes, preventing the player from getting "seen" entries for them. However, someone has obviously created a working code for Mega Diancie. My question is, if this is possible, would it be technically possible to create QR codes for legendaries like Necrozma and Silvally? I know very little about QR codes but if anyone has more information, or knows of a guide or a website with more detail, I'd be very interested. I've Googled the topic but using any phrase similar to "legendary Pokemon QR codes" usually just results in QR codes for PKHex injection, which is useless to me.