If anyone could post the electrical specs for an F12T8, that would be great!

Never even heard of that, do you know the physical length of the tube? I assume it is in between F14T8 and F10T8. If I had specs for the F10T8 I could estimate its ratings as being in between the 14 and the 10, but I can't find them anywhere. Of course being a T8 it's current is probably in the ~250mA range, assuming it isn't compatible with some sort of T12 12W version in which case it would probably be ~350mA. Voltage would likely be in the range of 40V or lower.

Do you have a F12T8 tube? If so I would love to see a picture

Edit: After doing some research, these F12T8 lamps are actually only 12.5" long making it even shorter than the 13.5" F10T8. This would make me think that the current is higher and the voltage is lower, but the gas fill is probably not the same so that is not guaranteed. So yeah I have no idea.

Here is a photo of mine https://www.lighting-gallery.net/gallery/displayimage.php?album=lastup&cat=14865&pos=1&pid=268131

It is the same length as my F10T8s but yeah I also don't know their specs. With the unusually sized tubes length sometimes varies between brands. I looked up a lot of things like "NEI F12T8" and stuff but there was nothing.

As far as I know, the 13 inch F10T8 tubes have an arc voltage drop of about 45V and an operating current of about 230mA according to Japanese catalogs I have read through.

The closest thing I can find to this is an F12T8 that seems to be one of those weird blacklight tube formats and is 12” long, but that has already been mentioned here.

There’s also an old format called the F13T8 that is also 12” long but is 13-watts. I believe that lamp is used in things like vending machine signs, display cases, and grocery store refrigerators, basically anywhere a very short but bright lamp is needed. But again, not 13.5”.

It is very much possible that the lamp was made for a very specific fixture. Small special-purpose fluorescent fixture manufacturers were designing proprietary fluorescent lamps all the time. I have seen some real oddballs. It’s likely that this is one of those proprietary lamps and information about it just doesn’t exist online.