Regarding the instance when Q was asked if the Earth is flat, and answered No. There's a school of thought that Q, not ready to make full disclosure of the truth on that particular topic at that time, opted to reply in the most straightforward way, and yet remain truthful. Because no, it isn't perfectly smooth and flat. There are hills, mountains, valleys...
Thus Q was able to speak the truth, without fully disclosing the truth.
Interesting theory.