I don't feel that the presence of a so called "pigtail" on the glass is indicative or attributable to a single manufacturer. It appears that the glass shear was dull or damaged and a small fragment of glass was left due to the inprecise cut-off of hot glass. Machine-made marble making was/is a huge volume business where the equipment will come out of alignment or develop small (and large) faults during the manufacturing process. I have vintage marble machine parts that show all kinds of wear and breakage that clearly affected the final product.
I wouldn't focus so much on the pigtail - but rather the glass.
Alan
