The Ampair 600  wind turbine assembly has been modified to suit as a benchmark structure in the pursuit of finding best practices for experimental substructure coupling of structural dynamic systems. Seven such systems have been assembled in test laboratories in Europe and in the USA. We scrutinize the dynamic behavior of the total assembly of three of those by vibration testing and compare the test outcome from seemingly identical assemblies. The aim is to support future component synthesis activities with high fidelity data and support future model validation. Comparisons are made by evaluating deviations of measured frequency response functions, the differences of identified structural eigenfrequencies and the correlation between eigenvector estimates. The testing is made in two parts. First, a partly assembled system, not including the hub and blades, is tested. This constitutes one possible and logical subsystem splitting that is likely to appear in future substructure synthesis efforts. In the second part, the full system assembly is tested. The test procedure, the test setup, the obtained test data and test data statistics are presented.