You're right, that is a good example where it would matter, but systems that are that close to the margin are probably pretty rare.
A system that was running that close to the margin where SWM channel assignments mattered likely wouldn't be able to do whole home at all, since the DECA tolerances are much tighter than that of SWM.
Your use of "likely" I couldn't disagree with, "but" once again "not always".
I could probably compose a system that DECA would work, while the high end of SWiM might not.
I don't think anymore "would plan" [or should plan] a system this poorly, but it's conceivable an "installer" might have connected one.