My point exactly was that when criteria are met, the shtar mechirs is effective, and it’s use existed long before R’ Feinstein.
Le ma’aseh, Rabbi Israel Meir Steinberg and others follow this shita, whereas R’ Soloveitchik wasn’t fond of it on policy grounds. This was actually a case where Reb Moshe was more meikil than R’ Soloveitchik.