The movement of the VB month to month, and whether a region becomes current or not is a calculation performed by Charlie O. As inputs he looks at how many visas are available, embassy capacity and demand (cases that are DQ). Visa availability is sort of divided into quarterly buckets for a rough guesstimate, so that they would not try to do 100% of cases in 3 months. Embassy capacity may be affected by Tier4 in the calculation, I can'yt be sure.
Last year went current because KCC controlled (and throttled) the pace of cases going through the DQ stage. So - the numbers they reported to Charlie O were very low, even though there were many cases that had submitted their DS260s and were waiting for documents to be processed. They failed to process cases in appropriate volumes, only asked for documents when cases were near to being current and so on. They also cut back on the speed of processing while DV was affected by the bans.
If KCC process documents at "normal" speed, and if there is a constant flow of cases hitting the ds260 and document inboxes, then it is likely that demand would be higher than visa availability, AND capacity could be limited by the tier 4 prioritization.
Assuming NO capacity problems (a dream at this point), and if everyone that submits a DS260 (usually about 65/70% max), ALSO gets their documents processed, that would mean demand would be about 80k (of which about 10% would be denied). So - in that scenario, there would be final caps in some or all regions. That the the "mathematics".
But we don't know so many things. We don't know what will happen with Covid, embassy opening status, if and when tier 4 gets removed, whether people get the message to #sendthebloodydocuments, whether DV2020 or DV2021 process causes impacts, whether KCC #processthebloodydocuments more efficiently and so on, or even whether people are so fed up with the DV process that the response rate is lowered, whether embassies will enforce the passport rule causing higher refusals. Way too many factors. So - whilst we could do the math, that doesn't help predict what will actually happen.