You can assume all you want Craig, I have in fact gotten HH scott 6BL8's in a 222C.
(how they got there, from the factory or someone putting them there, guess away)
That's how I found out about those 6BL8's in the first place. (they came in an amp)
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As far as the tube dying prematurely I see nothing that would indicate such a thing.
Here are the in circuit measurement checks I made on an 222C while evaluating them.
(these are actual readings from an amp)
6GH8
Pentode section
Pv 60 (good strong tubes test this voltage, weaker tubes higher, I'd go as high as 75v)
sV 63
cV 1.67
Triode
Pv 272
Cv 66
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6BL8
Pentode section
Pv 70 (good strong tubes test this voltage, weaker tubes higher, I'd go as high as 85v)
sV 63
cV 1.5
Triode
Pv 259
Cv 76
There is nothing on those readings that are anywhere near maximum for the 6BL8 tube.
(plate to cathode voltage on the triode is less than 200v even with a max of 250v)
So why would someone use one? Because it sounds better and should have no problem
in the circuit for a 222c so they should be viable swapping tubes if you like to roll them.
(obviously sound is in the ear of the beholder, "some" will prefer a good 6BL8 in there)