Just to add another anecdote, I feel like the people I know who are able to whistle generally recall pitches very accurately, they just can't name the pitches w

Just to add another anecdote, I feel like the people I know who are able to whistle generally recall pitches very accurately, they just can't name the pitches without further training. Whistling isn't hard to learn, and it is easier to control pitch through whistling than it is through singing (in my experience). I feel like whistling can be very helpful in revealing "perfect" (or very accurate) pitch recall in people.