When people say “I could care less.”, what they mean to say is that they don’t care at all, so the proper expression is “I couldn’t care less.” Saying “I could care less.” means that one does actually care to a certain extent.
Did that answer your question, or did I muddle things more?
True; this IS how it is mangled MOST of the time; but a person CAN say...
I could care less.
and actually MEAN it!
Other than this; you did a fine job explaining the problem: no muddle found in your response at all.
(Watch out; or I'll get that Carry On meme generator thingy going...)