hello Pete - sorry, not a clue as to attribution...........from your description, would appear that this glass wasn't finished on a pontil rod, hence we'd not refer to your bump as a pontil mark. Only by finishing on a pontil rod, do we get either the pontil scar or, as is more often the case, a ground/polished depression in place of the scar.
Toward the end of their lives, some of the bigger names like Webb and Stuart did finish their glasses in what was presumably a quicker and more economical method of production - as opposed to older traditional method of using a pontil rod - which was more labour intensive.
Assume you've tried all the Replacement sites.