The practice assymetric accidents came down dramatically with a change in techniques about 1970.
It went someting like:
Never approach on a runway of less than 7500ft
VCR of 600ft, never below safety speed until VCR
Never below 125kts till 300ft
Flaps always below 100ft, and no flap until throttles closed.
On take off no simulated failures until 140kts or safety speed if higher.
Practice losses then became much lower.