I don’t think it’s this cut and dry. GRRM is a pantser, true, but he’s said the Hodor reveal was planned at the creation of the character, as was Jon Snow’s character, and if you read GoT again you’ll get a dream of a mountain crushing a viper putting the death of Oberyn hinted at 3 books before the character was even introduced.
However, he admits he has no idea how the Meereen plot was supposed to go. Which is part of why it has taken him 10+ years to wrap it up.
The books, moreso than the show, does drop hints that the Targ madness is in Dany. To the point my friend and I have argued about it since I got them to read the series. Which was back when book 3 was released.