MK100.0-pioneer and MK90.0-pioneer

I will ask for an explanation:

why MK100.0-pioneer-202101240849-NIGHTLY can have a clear name with a full date and MK90.0-pioneer-210110-RELEASE unclear 6 numbers?

Does the last rom MK90 have any defects that are in the current version:

what changes are there in the next MK90 releases? is it just about adding more security patches or also fixing bugs? LineageOS no longer supports the previous version.

Thank you for your understanding