The directory authorities no longer allow versions of Tor before 0.2.4.18-rc. But right now, there is no version of Tor in the consensus before 0.2.4.19. Therefore, we should disallow versions of Tor earlier than 0.2.4.19, so that we can have the protocol list for all current Tor versions include:
Cons=1-2 Desc=1-2 DirCache=1 HSDir=1 HSIntro=3 HSRend=1-2 Link=1-4 LinkAuth=1 Microdesc=1-2 Relay=1-2
For Desc, Microdesc and Cons, Tor versions before 0.2.7.stable should be taken to only support version 1.