It's also likely that the hole for the top is worn more than the bottom. If you can't tell the difference in weight it probably won't make much difference but usually the stiffer cymbal goes on the bottom. Usually a higher tick sound when hit lightly but a deeper overall tone.
I have a pair of K-Custom Darks which are really similar in weight although the bottom is obviously deeper sounding. I also have a set of New Beats where the bottom is nearly twice as heavy as the top. The more differential, the more pronounced the closing "chick" sound is.