It does invalidate the original meaning because no one uses America to refer to that landmass anymore (in English). Common use is what determines the meaning of language.
"Nice" used to mean simple or foolish, "Silly" used to mean blessed, and "Awful" used to mean worthy of awe--modern usage patterns have invalidated their original meanings in modern use.
>I understand that it's not ambiguous to many people, but it's ambiguous in my own mind because I do think of "America" as applying to the entire land mass.
And I think of Columbia as an alternate name for the US. It doesn't mean I'm going to get on a Colombian Spanish language forum and start making up new demonyms for them.