I've wondered about this too. Also it's apparently signed to the base 'WE Bang' (possibly JE Bang?), although I've personally never come across any glass signed by Jacob Bang, and he had died before the Kastrup/Holmegaard merge anyway.
Also, the signature described doesn't follow any Holmegaard pattern that I know of.
My best guess is that the signature is for another glassworks, and it's been stickered by someone at a later date.