[Arran]

There is actually a third style of tube that you don't run across too much Stateside, and those are metal spray/spray shield tubes. they were quite common in European and Canadian radios of the 1930s through to the late 40s (at least in Europe). I think that they were just starting to appear during the final two years of Grigsby Grunow, and maybe supplied in the aftermarket for a few years after that as replacements. In Rogers built sets, with octals, they were purposely designed to accept either spray shield, or metal tubes, pin one is connected to the shield on both types, and even suggested that the owner could swap metal tubes into his Deforest-Crosley/Rogers/Majestic to see if it enhanced performance. This is quite handy as double ended metal tubes are easier to find, and you don't have add an extra  shield. One thing that may differ with regard to GT verses single ended metal style tubes is the inter-electrode capacitances, the few I have encountered have larger inner structures inside the GT style tubes. Of course I would expect something similar between double ended glass, spray shield, and metal tubes since the envelopes are longer on the glass ones.
Regards
Arran