W-4P or W-4R for RMDs?

I always assumed that W-4P was used for RMDs.

I just became aware of the existence of W-4R.

W-4P is for periodic distribs from a plan and the -4R is for non-periodic payments.

Are RMDs considered periodic from DC plans?  Most of the participants' RMDs that I work with are pretty much on an ad hoc basis:  they take them at various times during the year.  I have one lady who takes quarterly payments totaling her RMD for the year, but most take just one payment at the time it suits them.

So, should we be using W-4P or -4R?

I thought I saw something that the 4R isn't yet required for another year, too. 

But I would suggest considering whether the participant is making one election (I want exactly my RMD amount every year starting now) versus the ad hoc (gotta italicize the Latin!) way that I too am more used to seeing.

IRS has released

• Form W-4P for 2021
• Revised Form W-4P for 2022
• New Form W-4R for 2022

Ascensus is reporting that the IRS has postponed required use of the two new forms until 2023 (i.e., the 2021 form an continue to be used until that time). 

Instructions for the 2021 W-4P do say that an election using that form will continue to be in effect until a subsequent form is submitted; I don't see anything else in any of the instructions that mentions any other delay in effective dates.

From draft IRS Publication 15-A (released January 13):

"Although the final redesigned Form W-4P and new Form W-4R are available for use in 2022, the IRS is postponing the requirement to begin using the forms until January 1, 2023. Payers should update their system programming for these forms and are encouraged to begin using them in 2022 as soon as programming is in place but may otherwise continue to use the 2021 Form W-4P in 2022."

So will the current election forms that we have on file now be grandfathered in?   Or do we have to have a new W-4R for all RMDs now?