Harley released with the wrong printing number on the barcode, it should have ended with a 1 not a 2 to indicate which print it was. The Batgirl ad was an ad sure and it was an error.
I'm just going off the top of my head on these but if I'm holding 4 comics in my hand that contain errors would you call that a bunch of errors or not?
I thought we were talking about errors that had an impact on the secondary market. If a small error happens in a book and no one cares, it will have no impact on sales.
While I'm sure there is SOMEONE out there who is clamoring to buy up all the books with Batgirl 1 error ads, it might as well not be in the conversation.