Adding to Maxi's post:
when executing the kbd method, the hand motion = b,b,d/b~n~b,d/b~n~b,d/b, like Maxi posted.
But when looking at the command input, you'll see: b,n,b~db~b,n,b~db~b,n,b~db~b, etc.
After the db input, there's a "hidden" b-input, caused by releasing the stick after hitting db.
This means there are 2 back inputs, instead of one.
It's like wavedashing, where you have to do crouch dashes repeatedly, so hand motion = f,n,d~df,n,f,n,d~df, etc.
But command input = f,n,qcf,n,f,n,qcf, as there's a hidden f-input, which cancels the crouch dash, caused by releasing the stick after doing a crouch dash.
So in order to correctly test Korean backdashing, the notation b,n,b~db~b,n,b~db~b,n,b~db~b, etc. should be inputted.