Things I know must have happened in the world of Harry Potter, though they are never strictly mentioned.

• Dudley Dursley's wife gave birth to a darling wizard boy 
• Vernon died shortly thereafter from shock

• Sirius Black had an affair with Madame Rosmerta while he was at Hogwarts that was quite reminiscent of The Graduate.

• Rose Weasley and Scorpius Malfoy fell in love despite their valiant efforts to hate each other.
• Parents not pleased. 
• Red-haired grandparents parents even less pleased.
• Blonde-haired grandparents never came to wedding. 

• Luna's husband died tragically while hunting a crumple-horned snorkack, and she mourned him quietly in a cozy cottage by the sea. It was years later that a lonely wizard moved in beside her. The two rekindled their old friendship and realized that they would be much happier married to each other. 
• And, yes, it was Dean Thomas.

• Severus Snape still to this day, curses Harry from his grave. Snape had thought he made it quite clear to Harry while he was living that he despised the scarred, arrogant troublemaker. Apparently not. Harry still had the gull to name his middle child after him. I mean, really.
• It was Lily Luna Potter, not Albus or James, that inherited her father's superb flying skills. She became Gryffindor seeker, and played just as well (if not better) than him.

• Cho Chang is a ninny

• Susan Bones dropped an egg carton at the supermarket, slipped on the slimy yolks, and fell to her death because she's that lame.

• Gregory Goyle was actually a genius, but just pretended to be half-witted to make his best friend and fellow crony, Vincent Crabbe, feel better about himself.
• This loyal mark of friendship went unacknowledged by everybody, including the Sorting Hat 
• Dumbledore had always said they sort too soon…..

• Peter Pettigrew refused any meal that wasn't mostly made of cheese.

• Voldemort died a 72-year-old virgin.

• Hermione told Harry that she stuffed her beaded bag in her sock when the snatchers came and took them to Malfoy Manor. Hermione obviously lied because that isn't possible 
• (unless she was wearing jeans)
• (I tried it)

• There were too many cats (as previously discussed)

• Death Eater, Augustus Rookwood, looked like the child snatcher from Chitty Chitty Bang Bang

• Cormac McLaggen always wondered who his father was. His mother refused to talk about it, and it was only after years of searching (and some reluctant help from Hermione) that he discovered the truth.
• But he was probably better off; Gilderoy Lockhart would never have made a good father.

• Pansy Parkinson had a mad crush on Seamus Finnigan but never told anyone

• Winky was never quite since her dismissal from Master Crouch, but was able to regain some of her former cheerfulness after being hired by her new master, Percy Weasley
• This act did not go unnoticed by Hermione who eventually had to accept it because Winky burst into tears every time she mentioned freeing the elf.

• Ginny and Harry had a dispute over the location of their future home…
• Harry didn't understand what was so wrong with Grimmauld Place, and Ginny was there rolling her eyes being all like, "Get real Harry".  And he was like, "Think about Kreacher! He loves that place", and Ginny said "Kreacher also likes Death Eaters and Sirirus' mom." An exasperated sigh from Harry followed. "That was in the past Ginny! He's changed since then. He makes like really good soup now." And then Ginny was all, "Fine. You and the seriously distrubed house-elf can live happily-ever-after in that grimy, dark wizard pen. I'm going to go get some fresh air," and promptly flew away on her broom, as Harry seethed from the ground.