Most glass is not marked with the name of the maker, this can be a problem or it can be seen as an opportunity for us would be glass detectives. As a result any remaining labels become very useful for identification.
Items may leave a factory without a makers mark for many reasons, perhaps the person who normally did that job was absent, the machine was broken or there was just not enough time to fulfil an order, maybe the buyer wanted it that way.
It is very pleasing when you eventually do manage to identify an item after a long time searching.
Sorry I can not be of any constructive help.
John