Let's consider the following example:

a) meta-layer-which-we-want-to-consume (contains: LAYERSERIES_COMPAT_clang-layer = "gatesgarth hardknott")
b) openembedded-core
c) bitbake
d) meta-our-layer

By saying that layer (a) required some extra bbclasses to be cherry-picked I meant that
in order to use layer (a) we had to cherry-pick some extra bbclasses or other changes
into (d) to get (a) working with (b) and (c).

This worked for us when (b), (c) and (d) were on yocto morty, but stopped to work when
we switched to dunfell because dunfell started to utilize LAYERSERIES_COMPAT.

This is very common situation that nothing needs to be modified in (a) to get it working with different versions
of (b) and (c).

So the question is why we have to modify also (a) to make (c) happy?