Jeff, what you have is not Griswold but from some other maker.  No.10 style popover pans are a common style with many makers having made them.  Sometimes a different number was put on the pan; Favorite, for instance, marked theirs as a No.4 but it was cast from a Griswold pan.  I kept a bottom gated No.10 popover in my collection because I think it is a neat pan.  Is the handle marked also with a "P" on it?  One of the old, gated pans is that way but I think there is also another popover without it.
Steve