“BCS Cooper pair condensation” is theoretical method that is used to explain superconductivity/superfluidity in fermion systems. If we treat “BCS Cooper pair condensation” as a physical phenomenon, then I do not know if there is a general agreement on what is this physical phenomenon. ie what is the definition of “BCS Cooper pair condensation” as a physical phenomenon? If we define “BCS Cooper pair condensation” phenomenon as the phenomenon of superconductivity/superfluidity in fermion system, then the “BCS Cooper pair condensation” phenomenon has been observed. But such a definition is not proper since there are superconductivity/superfluidity that has no “BCS Cooper pair condensation” (such as charge 4e condensation).
So, before answering if the “BCS Cooper pair condensation” phenomenon has been
observed or not, we need to define what is “BCS Cooper pair condensation” phenomenon in terms of EXPERIMENTS. This is actually a very tricky thing to do.
It may be worth while to start a new question: What is the “BCS Cooper pair condensation” as a physical phenomenon in terms of EXPERIMENTS?