Any synonym of "Left" works for me, "vacated", "leaving", "out of (American accent required)", "commenced descent", "departed", but "left" works well...
It's the advice that's important, not the words used, as long as there is no ambiguity.
I work in radar, lack of advice of leaving a level, tends to leave me getting an 'approaching FLXXX" call, (response to self well if you have said "left FLXXX" I'd have giving you lower...), response to you "descend FLZZZ" This is especially common when you've had a when ready descend advice and you take more than 5 minutes to descend; i.e. I don't need to look at you (in terms of next task) until you call "left FLXXX".