Some dictionary definitions (https://en.oxforddictionaries.com/definition/extempore) of extempore I found allow only without preparation:
Spoken or done without preparation.
Some (https://www.merriam-webster.com/dictionary/extemporaneous) allow also the other meaning without notes:
a (1) : composed, performed, or uttered on the spur of the moment : impromptu an extemporaneous comment
(2) : carefully prepared but delivered without notes or text
c : happening suddenly and often unexpectedly and usually without clearly known causes or relationships
b : skilled at or given to extemporaneous utterance
I have often heard using the phrase speak extempore as speak without notes. Also one of the questions here on ELU uses the word in this meaning: Antonyms for "extempore" — speak without notes.
Can I use the word extempore when I want to underline the fact that someone is speaking without notes, and still well prepared? What would that word primarily mean if I just say "The mayor had an impressive extempore speech"?
I am confused - the M-W definitions a(1) and a(2) seem to be in conflict.
"Multiple distinct meanings" are OK, but "multiple (almost) opposite meanings" are confusing, especially for loanwords, where we often use a loanword for increasing precision of expressing, like in technical language.