Surprisingly, forum search didn’t show anything. My question is not the meaning, the logic or lack of same, which is “better”, or
whether one or both are ironic. Those topics have been well beat to death elsewhere. What I’m after is any information about first uses both in print and in undocumented speech.
There is an argument raging quietly in another forum about the age of these expressions. Printed ‘first use’ for the couldn’t form has been
stated as 1940s, with the could version coming a couple of decades later. Yet one of the best informed members attributes his use of “I could care less”
to childhood, and a Scots-Canadian grandmother. He is about sixty. His statement follows:
My source of the expression is my mother, whose variant, learned from her Scots-Canadian mother, was so conservative she still said thinks like “I hied me” instead of “I hurried.” [...] The point has been validly been made that provincials and colonials sometimes preserve idiom now long-forgotten in BE, but current at the time of their emigration from the Home Isles. For my mother’s family that would be somewhat early in the 17th century.