0.19 and 0.20 being released closed to 2019 and 2020 is a coincidence. They just mean a new release that will be supported longer term with backports when needed.
Regarding the minor version, an even number means a released version while an odd number means a devel version. So there is a 0.20.0 and a 0.20.2 but 0.20.1 was never released an corresponds to the devel branch between 0.20.0 and 0.20.2. Note that since only bug fixes made it to 0.20.2 there are a lot of commits done in 0.20.1 that will only be merged in 0.21.0
