Michael,
That is not a stupid question! However, my answer may be!
I assume because you mentioned license plate lights, that you are referringh to your rear bumper. If the holes are evenly spaced and are on top of the bumper, they may have been where the license plate lights were mounted on an earlier car...so you probably have a replacement bumper which came from an early Kammback (I think 71 & 72) car. They had the license plate lights in the bumper (I believe).
If anyone knows better than I, please jump in! I can't really remember if the bumper mounted lights were only on the GTV or if the Spider had them too.
Cheers,