If there is an overlap it's usual for women's clothes to be right over left and men's to be left over right but that doesn't alter the zip. It's the same with trouser flies, women's go right over left and men's left over right. If I wear a 'unisex' garment constructed the men's way it feels really awkward to fasten. However, I've just made
these jeans and the pattern said to have the fly overlapping left over right. I didn't, I it the conventional way!
For a jacket you have the opening end at the bottom and the pull will be on the side it is - unless the pattern specifies a two sided/reversible zip which can be opened/closed from either side, and in that case I can't see why the pull has to be on a specified side.