Mike...There is a "worn" area on each. The pic shows what I think you're trying to describe. They all measure the same in a template. The thing that got me thinking they may be "mold" is the grainy looking texture of the glass. It looks like a wood grain, but not orange peel, if that makes sense? and then that line that completely circles the marble.
Galen, would the odd looking worn area in the pic be what you're describing? It looks like it was was ground down in some way.
Thanx..................Steve