I honestly don't know. I received my replacement recently and when I asked if elrog fixed the problem, the answer was yes, but when I inquired for more information, he doesn't know specifically what elrog fixed.
But, elrog is offering me 2 years warranty, so think I good, except my attempt to contact elrog haven't been very successful, haha so... We'll see.
Please let us know if you have any further issues with the ER300Bs.
Do the bases look any different than the failed tubes? A theory on the failures that has been put to me is that Elrog made a change in the bases that had poor pin alignment, putting stress on the tube leading to early loss of vacuum and bad things happening. If the bases have been changed that might be a step in the right direction.
[disclaimer - this is all hearsay from me - I do not own any Elrog tubes at the moment. I would like to, once I am confident in the product]