Thanks

I did call EFTPS and they gave me the "March to Nov" months that work with Def SS pmts, but no explanation.  The individual I spoke with basically read off the FAQ at the top of this link: Welcome To EFTPS - Help and Information

I don't think any letters have been sent from IRS to Self Employed folks who deferred, nor do I think they will.  The link you provided says "If the installment amount is not paid in full, IRS will send the taxpayer a balance due notice.", so I assume that will be sent AFTER Dec 31, 2021 and probably include some penalty, so I want to be sure clients pay prior to Dec 31.  

Thanks!