If a clue has at least one space, or one hyphen, or a slash, or an ampersand, or if a clue has at least one period in the middle of a clue, or if a clue involves separate individual letters (i.e. NBC, JFK, etc.), that would be illegal.
Apostrophes do not affect clues in any such manner, therefore those clues are perfectly acceptable.
Not sure about acronyms such as Exxon or NAFTA, though.