The pieces of wire you are referring to are called the getters. I have 2 pairs of 421as. One pair from the early '60s has "D" getters on the bottom. The latter pair from '78 has a "O" getters on the bottom. Both pairs have charcoal plates but the older pair also is a bit taller with slightly larger plates. So as far as I can tell that is the pattern, earlier 421As "D" getters, latter ones "O" getters.
I formerly had 2 pairs of TS 5998s and both had the shiny black plates that definitely look different than the plates on the 421as. I sold those off.
Do a sound test. I found the 421As superior........by a good margin. Larger soundstage, layers of air, increased dynamics and imaging, but yet an amazing delicacy that made its sound signature irresistable and the top power tube I tested, surpassing even the very excellent GEC 6AS7G.
**Edit note: Despite the difference in construction, I found both the early '60s tubes and the '78 pair had practically identical sound signatures.