What does it do it you put each chip into the different memory slots?
I could envisage a "dead slot", or I could envisage an addressing issue in the memory controller where it can't go above a particular address, regardless of chip position.
I could also envisage the "that one doesn't work in this machine" that LR mentions with valves. I have a perfectly good RF pentode that won't work in my Quad FM tuner.
I haven't changed any memory chips in a long time, so the ones in my "bits" drawer in the workshop are prehistoric/obsolete (like me, I suppose).