For the accelerometers the problem was the tiny tilting of the sensitive axis in the gravity field. In this case you're probably right that this doesn't matter -
but in general it is difficult to rule out every second-order effect when the forces at play are so small with respect to g.
OK, that I guess that kinda-sorta makes sense if the accelerometers were rigidly mounted to the floor. Was that the case? Because if so then what you would have would basically be a seismometer, and floor bending from the test masses would, it seems to me, be the least of your worries.
Yes, the accelerometers were mounted on an optical bench and of course we could detect any minor earthquake (sensitivity was around 1e-10 ms^-2).
The bending of the floor due to the presence of people in the room was noticeble indeed.
