After all that washing it was certain that you wouldn't have any flakes.
I use castor oil almost daily for over a year (not massage it) and leave it to my hair all day cause I want to have that wet look and is like a gel.
If it worked I wouldn't have any dandruff but I have.
The only think that really works eith dandruff is ACV (apple cider vinegar) pour it to your scalp (mixed with water- I prefer 1/3 acv 2/3 water) and leave it.
Do it at night before sleep. The smell luckily will be gone the next morning.