The intervening years 1920 - 1923 are messy with national and regional differences in government persisting, sometimes reflecting greater or lesser willingness of local populations to accept Bolshevik rule and with it subordination of some kind to Moscow. In addition, economies had collapsed, people had starved, many had gone into exile.
Mail from this 1920 - 23 period outside the core RSFSR often reflects the difficulties of transition to Soviet rule
Here are two examples that I have recently acquired.
The first is a Registered cover sent from VINNITSA ZABUSHE POD[olia] 17 3 20 and addressed to Petrograd with PETROGRAD 3 4 20 receiver on front at top right and a Petrograd 6th Expeditisa cancel in red on the reverse. At the left on the front are the remains of a SPRAVKA form: the letter could not be delivered and arrived back in Vinnitsa on 19 4 20. This is just prior to what would become the Polish Occupation of Podolia during the Russo-Polish War of 1920
The 10 rouble franking with Imperial Arms stamps overprinted with Podilia type 1a Tridents is interesting: it is the correct RSFSR Tariff introduced in Mocow and Petrograd on 10 March 1920 but often delayed elsewhere because of lack of notification. Here the Notification has clearly arrived. When the collector and dealer pencil scribbles are removed from the cover, this will be a very nice item
There are two puzzling marks on the front of the cover at bottom right: a small violet circular cachet with a number inside and a blue circular seal. It is this kind of thing which adds to the difficulty of understanding mail from this 1920 - 23 period. I rely on readers to provide information about them:
Neither 500 or 1000 corresponds to an RSFSR Tariff so I have to assume that this is a specifically Georgian Tariff. I await further clarification from readers.
Added 25 February: Alexander Epstein writes to me that this cover is sent from Abkhazia during a period (March - December 1921) when it was Sovietised but virtually independent of Georgia. Later it was federated with Georgia. Georgian mail in 1921 is very scarce (as Dr Ceresa has also observed), but Epstein says that this is the only 1921 Abkhasian item that he has seen: