Long-Neck Bottles with Sticky/Rough Shoulders

I was soaking bottles in Oxy to strip labels and came across a handful of bottles that I couldn't get fully clean. It seemed like the glue residue on my plastic scrubby might have adhered to roughness on the shoulder of the bottle. The rest wiped clean without much effort, but the shoulder seems physically roughened and won't become clean of glue. Some others seemed they might have already had this condition before I used the scrubby.

Not sure exactly which bottles, but it is likely they had a shoulder label (in addition to front/back/neck). Could this label have etched the glass? Or used a different adhesive that won't come off?

Anybody encounter this?

Aaron