How far back does "recorded history" go for these sorts of detailed space weather measurements? The linked #8 ranking seems to be based on 20 years of data

As far back as the Carrington Event at least.

https://en.wikipedia.org/wiki/Solar_storm_of_1859

I think they go back to the early telegraph based off of observations of static on the wire and other related problems (a telegraph was basically a giant inductor).

Are those classifications listed somewhere? I suspect that they'd be much less accurate than the measurements from modern equipment (e.g. satellites)