Good question(s).
I assume (meaning, make an [censored]-of-You-and-Me) that it means that the same part was, in the years designated, installed/displayed on the left of the lower endgate and in some years it was installed/displayed on the center of the endgate.
My assumption is supported by any/no same rear-lamp not being listed for any other location for the same vehicle in the years designated. And, no other rear-lamp is designated for those vehicles.
Apparently, that lamp swung/swang/swanged down in either location?
