GMAT Strategy

Does the time of year you take the gmat effect your score/percentile? Like if you take it after the deadlines for b-school, is the competition less and could your score or percentile be better? (and do scores and percentiles not necessarily match, like percentiles don't necessary correspond to one score right?)

I think someon asked this before but i can't find the thread so if you can elaborate that would help a lot.

thanks