Tau pathology precedes Ab deposits

Tau pathology can be observed without Ab deposits in non-demented patients (rare but possible event).
Ab deposits are always observed in the presence of tau pathology, at least in the entorhinal cortex.

Delacourte A et al. Nonoverlapping but synergetic Tau and APP pathologies in sporadic Alzheimer's disease. Neurology 2002; 59: 398-407.

To understand this interaction between tau and Ab, lessons can be provided by other tauopathies