It's plenty, because 30yrs is usually the rule of thumb for enough, and extreme events are more likely to be recorded even in the absence of/before there were r

It's plenty, because 30yrs is usually the rule of thumb for enough, and extreme events are more likely to be recorded even in the absence of/before there were regular record intervals. There are well established probability distributions for these things, so you're really just solving for which published curve and maybe a magnitude multiplier and seeing where your data fits. Also there's uncertainty baked-in and accounted for at every step of the engineering design process. Eg. Geotechnical engineers love to calculate 6 digits to 4 decimals then throw in a 400% factor of safety.