[Milsurplus] 4CX250 varations

[Mike Durff via Milsurplus]

Looking at my latest project, an AN/URC-32 power amplifier, I see that there are many variants of the 7580 / 4CX250B. Other than the obvious differences in filament voltage there doesn't seem to be much difference in the specs. 
Question 1. Why so many different 4 digit numbers for this tube type?             2. Will the differences in this tube (mainly variables in inter-electrode capacitance ) make much difference when operated at HF?
I do not have the complete AN/URC-32, nor do I want one. I mainly interested in the PA.Thanks, Mike, K4TQF