Hi Nick,
Thanks for the feedback regarding the base. I agree that a sleeve has been soldered on but I have to believe this was done at the lamp factory (or perhaps by US&S Co.) because of the quality of the solder joints. I have seen at least three other similar bulbs with the same two-piece constructed base. I?ve also found the bulb and this base illustrated in some old US&S Co. literature (see attachment below). In this literature, they refer to the base as a ?special rebased base? ? not sure exactly what this means though. I don?t think there are Edison threads underneath the outer sleeve, but rather this seems like some type of modified precision pre-focus base.