For Decred, 20k units per month is factually wrong. At only 20k miners at 2TH/s each would result in network hashrate of 40,000TH/s. We are around 25-30,000TH/s right now.
I think 5k units per month is more like it, add to it what Ibelink is adding.
Wisdom aside, 20k units in 2 months would mean we should be at 40PH, but we are not there. The actual number should be 5k x 2 months = 20PH. What is being added is mostly Ibelink 6TH units, I think they are testing and slowly dispatching them, which gradually pushing up the net hash. Who know where the net hash ends up. If Ibelink adds 5k, we are looking at 40-60PH, plus more when oblisk ships.