Differences in #40 Monophones?

[HowardPgh]

I have several AE 40s and I noticed several differencces in the internal wiring.
Mainly I see that some don't have the two terminals molded in the case by the hookswitch and there appears to be more soldered connections.
Some have seperate condensers for talk and ringer. What is the thing that looks like a rubber bumper for?
Are felt bottom ones older?