The master server already filters out any older versions of Blockland, so they aren't shown on the master list.
no it's possible to overcome this
Yes! BUT
WARNING: Do not host a v20 server (LAN is okay) but Badspot will IP ban you because the server is pointless and not accessible for today's Blockland v21
yes, but you can host v20 servers fine if you use port's v20 download, as it uses a custom master server.