[Boatanchors] Question for Tube Testing: 6DJ8

[William Morton]

Hello All,
I have a Tek 545A which has a boatload of 6DJ8 tubes in it.  I took some out to test on my Hickok 605A, using the settings in a consolidated Hickok setup document found via a web search.  All of the tubes tested low or nearly dead.  Further searching found various discussion threads mentioning the difficulty of testing 6DJ8 tubes on Hickoks, but no in-depth details.  I have a Seco 107 that also has settings for 6DJ8, retested some them and they were fine (unless the Seco was lying to me).
My question is:  Why are these difficult to test on Hickoks and are these difficult to test in general?
Also, in my web wanderings I also found information regarding E88CC, which I thought was a typo for the European designation of the 6DJ8 (ECC88).  The numerical designation for E88CC is 6922.  Now it looks like there are 4 designations for the same (?) tube: 6DJ8/ECC88/E88CC/6922.  Ah, so much to learn....
Have a great day.  Helpful comments would be most appreciated.
Best Regards,
William