Very Loosely Based on a True Story: The story goes that Andrews got the inspiration for Flowers in the Attic from a doctor of her's that she had a crush on, who supposedly (along with his siblings) was locked up in an attic for several years.
What Could Have Been: The first draft (which was donated to Boston University after by Andrews' mother in 1993 after Andrews' death, among other writings and notes) was titled Open the Window and Stand in the Sunshine. As a Mythology Gag, the prologue (the first draft lacked a prologue) to the final draft has Cathy briefly considering titling her story Open the Window and Stand in the Sunshine, but remarked that she and her siblings were more like "flowers in the attic" instead.
The 2014 TV movie provides trivia of:
Billing Displacement: Like the 1987 movie, the actress playing Cathy is billed after her mother. Kiernan Shipka is actually billed third after Heather Graham and Ellen Burstyn. It's the same in Petals On The Wind, where those two get billed above Rose McIver.
Kiernan Shipka (outside her more mature, complex role in Mad Men) is largely known for playing the precocious, good-humored Girl Next Door. Her role as Cathy seems almost a dark parody of her usual trope: the Girl Next Door in Danger.