20DP4 and 20CP4 are they interchangable

[dieseljeep]

I always understood that was the slight differences in numbering codes was the manufacturers practice to differentiate their product, from the other makes.
Didn't all those CRT designs, have to be registered with the RMA or RETMA, at the time?
BTW,I never ran across, any of those CRT's listed in the text, like the 20" numbers.