The most comprehensive cross-validation is that Chandler wobble, ENSO, QBO, and several other climate indices can all be straightforwardly interpreted as tidally forced behaviors. Cross-validation via parsimony says that since one model can explain many diverse behaviors simultaneously, it likely means that is indeed the correct explanation.

FYI, I presented this idea at the 2018 AGU, download the PDF which describes several possible cross-validation approaches

https://www.essoar.org/doi/abs/10.1002/essoar.10500568.1