I never hear of an individual that wants to superfund a 529 for less than 75K but more than 15K for the year - is it all of nothing on the 15 or 75K - if over 15K but less than 75K do you need to use part of your gift tax exclsuion?
I bet all the information you are seeking can be found here:
https://www.savingforcollege.com/article/10-rules-for-superfunding-a-529-plan
