I think a journey with multiple agents to collect information would give you a more complete picture on data points.

Ask for DNA and what is known.

Climate records and what is known.

Town losses and movements. In some places inhabitants seemingly moved way way up the mountains all of a sudden. This is usually associated with conflict or tidal waves.

Migration evidence.

And any other disease or food shocks.

One must also be careful to understand the data observation process and to justify any belief that the collapse is not merely absence of observations.