I think these numbers relate to the build version number, e.g. my Nokia 8 has build version 00WW_4_84A_SP02. Unfortunately I don't know what the build version on previous Android versions was.
So whilst HMD are releasing some of the kernel source code, they're still far from perfect. Several phones have still not had a release, even though they were released a while ago, e.g. Nokia 5, Nokia 2.
Also, not all software versions for each phone have been released, as far as I can work out. The security patches page gives a clear list of the different versions of software for each phone: https://www.nokia.com/en_int/phones/security-updates
I've worked out that we can easily cross-reference the version numbers of the source code releases with all the released versions of firmware by HMD.
The security updates page lists all models and all versions of their firmware: https://www.nokia.com/en_int/phones/security-updates
The source code page lists all releases of kernel source code (AFAIK, HMD have not released copyleft source code for other parts of the firmware).
One can easily see that HMD are not releasing the source code for each version of the firmware for each phone. This may be because HMD are not updating the kernel with each software release, however this would be surprising between different Android major versions. This means that for the Nokia 8 I think they should also release at least the source code for Android Nougat and maybe also other firmware versions like they have for the Nokia 6.