The release numbering is really simple, just without the meaning you mention.
It follows the <4 digit year>.<2 digit week number>.release.sub-release
So 2019.20 is from week 20 in 2019, simple as that with no dev/test/prod significance.
It also doesn't signify anything if the release has four parts, 2019.20.0.1 has been identified as a having enhanced summon, but that numbering format doesn't signify as such.
In the past year my car has had both odd and even numbers as well as two, three and four part release numbers
For example amongst the 22 updates there have been
2018.42.2.1
2018.50.6
2019.5.4
2019.5.15
2019.12.1.1
etc etc