DB RMD - changed the plan year during 2020

Hi

Having a discussion and curious about the following for a 2021 RMD:

Plan year changed during 2020.

9/30/2020 AB 2000/monthly

12/31/20 AB 3000/monthly - short plan year from 10/1/20 to 12/31/20

What is the AB used for 2021 RMD?

Another scenario

9/30/2020 AB 2000/monthly but 20% vested at 400/month

12/31/20 AB 3000/monthly - short plan year from 10/1/20 to 12/31/20 but 40% at 1200/month

What is the AB used for 2021 RMD?

Thank you

Hi, any takers?

Thank you