Whenever a client has an unusual item that affects the following years I note it with a sticky note on the inside cover of their tax file.  For instance to look for DCB or which year it is their turn to claim junior or if they deferred casualty gain.  So I have yellow sticky in front of all who deferred reporting 100% of 1099R.  I suppose you could have someone go thru each 2020 client to see if they deferred 2/3 and write a sticky now to put in their file?