Don't know about the 12A family, but I did a bit of rolling when I had an ARC SP10. Very good were Telefunken 6902, but standard T 6902 were almost poor beside the Telefunken 6902 specially selected by HP. They came with both T and HP seals.
Rumour in 1970's LA was that engineering co-op students spent a lot of time at HP testing tubes, discarding more than 95% to the dumpster. Which explained why HP want 10x the price for their tubes.