I guess that explains it, while the designation might sound official, I failed to find such a lamp when I took a look in some of the literature on Lamptech.

Yeah generally most LP sodium luminaires that would normally use a base down lamp such as a post top would instead use a frame to mount the lamp base up instead. I guess there are some fringe cases where this would be undesirable (frame blocking light and leaving a shadow on the globe for example) but the market for such a lamp would probably be minimal to warrant designing and manufacturing a lamp with a inverted discharge to allow for vertical base down operation.   

We find that there's a very minimal shadow cast from the frame on Gemma, it all comes down to how good the refractor is at filling in the blanks... 

I can confirm that an SO/V lamp never existed.  Neither did an SO/D or SO/U.  All types, right since the very beginnings of lab trials prior to manufacturing, were developed for horizontal use.  However the lower wattage lamps can tolerate being burned from cap up until cap slightly below horizontal.

It is just practically impossible to prevent the liquid Na from touching the lead wire seals when those seals would be the lowest part of the arctube.