Vs0 is the minimum speed demonstrated in a stall, and the aircraft can actually be below 1'g' during the manoeuvre with the result that the aircraft wouldn't actually be capable of sustained level flight at Vs0. Consequently it's sometimes called "Vs-min"
Vsr0 is the minimum speed corrected to 1'g' flight - which means each speed is corrected for the instantaneous 'g' and THEN you take the minimum - or, alternatively, you can work out the lift coefficients during the manoeuvre, then take the maximum, then calculate Vsr0, because it's basically the same thing.
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