Do pendulums lose accuracy from seismic activity, people stomping on the floor, etc? Or does the nature of a pendulum naturally absorb that sort of interference?
If I had to take a guess the reason is the only coupling through to the pendulum would be via the friction in its bearings or via movement of the air around it. Both of these are naturally minimised in most designs so normal vibrations are not an issue.
Long-term performance depends on:
– temperature (absolute, relative, gradient)
– atmospheric pressure, air currents
– humidity
– shock & vibration (air, ground, wall)
– material stability or other disturbances
– energy loss stability & energy gain stability
While I'm not trying to claim it has no effect, the effect must be slight enough as to be negligible, otherwise we'd have seen some kind of compensation as we see compensation for temperature, spring tension etc.
Perhaps I'm underestimating it though and the reason this is not compensated for is simply that these where the atomic clocks of their time. They would represent a significant investment, no idiot would install it in a building set back from a major truck road or expect to be able to run tap dancing classes in the room above. It's quite likely that the manufacturer set out standards for the building it was installed within, perhaps even down to the type of foundations it had to have.