As I said before they are related in some sort. to explain more what I am thinking about the selection process, let's take an example:
Nigeria had 1,356,396 entries in DV-2013, the probability that a nigerian got selected is very high. the total entries in the world 7,941,332 (I don't have Africa to prove more what I think). As I said the probability that a nigerian got selected is about 17%, and in Africa is more let's say 30%.
so when the numbering starts, lot of nigerian showed in the first thousands CN. The fact that there were no CN of nigerian beyond 20000 is because of the limitation 6000 selected was at about 20000 CN.
17% nigerian on the real selectees witch was 109000 had no purpose, so limit on selection is a must as we all know.
and if nigeria is very present in the first thosands, it will be subject to special cut-off just to slow down interviews.
Now, after 20000 CN, each nigerian CN will be disqualified creating a hole in the numbering and that's explain the holes number evolution in the chart. because when a country reach it's limitation the graph of number of Cases Drope suddanly and in the opposite the holes graph incrrement suddanly, we can see that with nigeria, egypt, ghana and Ethiopia.
When i saw the EU chart, i saw Uze and Ukraine limit and another country witch i didn't identify yet.
iran case is special as interviews are spreaded among 3 consulate so slowing down interviews will be according to 3 consulates capability.