Vs1g came into being about the same time as the A320 initial certification.
Previous stall speed determination was the "minimum speed during the stall manoeuvre".
The problem with this approach was that all aircraft were not equal once flown beyond Cl max. Aircraft with the same Vs1g do not necessarily have the same Vsmin. This was to "level the playing field".
Had this not occurred Airbus could have still demonstrated a Vsmin stall in flight test.
Pretty well all stall testing is done at an approach rate of 1 kt/second, this results in a descent, also the higher the approach rate, the lower the stall speed.
The new factors were chosen to be the equivalent of the previous factors.