Thought I'd post some pictures of the CD 321 in my collection... it has a small protruding ridge around the inside of the base. A couple of these have turned up lately that have an extreme amount of this protrusion... I think it is caused by excess glass in the mold, leading to the mold parts sliding to accommodate the excess glass. If the amount of glass is smaller, the inside mold piece will adjust even further to make a small vertical inside edge that goes up inside the skirt, sort of the opposite of the protruding ridge. Hard to explain, wish I had a diagram. Think of telescoping concentric tubes.