If you look close, most circlips do have a sharp, 90-degree edge on one side, and slightly smoother, rounded edge on the other. In some
applications, it does matter which side is used, but not on these mowers. The circlips can be fitted either direction, no problem.
More important is to make sure they are not stretched or bent and fit properly. If in doubt, replace. They are cheap, and it is a lot easier to go ahead and replace when you have everything apart vs. having one pop loose after you get it all put back together.