Hello,
Lets say there is a bug in a package X, however package X is still usable by itself.
However package Y depends on package X, and as a result of this bug it was an RC bug.
Is the bug against package X also RC?
My reading of the criteria is it depends on your interpretation of "makes unrelated software on the system break". What does "unrelated" mean? In this case it seems they are related as package Y depends on package X. Or maybe it means "unrelated" as in generated from different source packages?
If the bug against package X is not RC, this restricts the ability to conduct NMUs against package X if the package maintainer is not responsive.
(I am deliberately not referring the any real life examples here because the real life examples are a bit more complicated, and this may distract from the basic question I am asking)
For example, X could be a library (glibc?) and Y could be a package that breaks due to some regression in X. Or X could supply a plugin for Y and Y changed/fixed the API breaking compatibility with X.
Also for simplicity, assume that X is already fixed in a new upstream release or the change is a simple 1 or 2 line patch required to fix the problem.