IIRC the only pure-neon tube about that size had a return electrode for each segment. as otherwise the strike voltage needed to ionize the neon would be insane- and the current would indeed eat the electrodes for lunch.
Mercury and the other trace gasses added [like Krypton] help the initial ion path form.
Adding the toxic elements after the tube is sealed to avoid worker exposure makes a lot of sense.
I think someone answered this- called a 'giver'- it's what the mercury and whatever else was in so they could purge, fill & seal the tubes with pure neon, then use the heating element to melt them free after the touchy part was done. cheaper & safer.
I came up the for-sure last bits from my supplier.
a matched set of 4 'antenna' B7971's with white Burroughs print, hand-assembled [inferred- they wouldn't shift back from the printed circuit-on-mica, right?] nickle ribbon construction. and a used socket.
now I need to price 'em, the last I sold I got $150 for... I need to check the market..