The matsushita dual triodes that 'flash' tend to be the ones that are mullard based. You can get duds from any tube, even the exalted ones. I bought a pair of triple mica 'forever' Siemens a while ago, hoping they would be plug 'n forget in my Wavacs. One of them blew out in a couple of days. I found the other one in my tube stash recently, tested it, and only one triode half was operational. They had been advertised as NOS at a pretty penny and looked very nice.
Yes, a lot of tubes in the day were extremely incestuous in labeling and parts. It is not unusual to see a 'matched' pair on ebay with different labels i.e. Westinghouse on one and Ken Rad on the other, with identical anatomy.
One of the interesting 'blind shot' tubes were the ones with the heavy RCA red label, that could be telefunkens, mullards, amperex, siemens etc. Many Radio Shack tubes are likewise from the 'desirable' factories. Somebody who is intricately versed in tube anatomy can pick out great 'mislabeled' bargains by looking carefully at the photos.
One of the strange tidbits of tube history is that in the day, Americans valued USA manufactured brands and considered the European brands to be less desirable or unreliable, so the euros were often bulk sold and re-labled because they were 'cheaper'.
Heh, Heh, now you have veblens audiophiles tripping over each other to throw big money at the NOS euro brands with their contingent mythologies.
