Further tiny bit of evidence. The pinch was completely replaced with a modern soft glass one. Hence the need for a graded seal. So the final anode was the only original pyrex to metal seal that remained.
This is a bit of a long shot, but if the pinch from an old pyrex CRT is saved, it could be attached to a vessel and pumped. If this is done in an oven and leaks are found that's reasonable proof that pyrex to metal seals don't like being re-heated. If leaks aren't found then it's simply inconclusive.
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