I have a QA flagged cecha01 on cfw 4.21 downgrader, I haven't been able to downgrade.
Also from what I read at tortuga cove you can toggle qa on in 4.21,
some guy on the forums did it (I haven't tried it mines was already toggled on).
That guy was able to downgrade, but for some reason I can't lol
I've tried both the rogero 3.55 pup you are supposed to downgrade with and ofw,
my ps3 kept telling me it was on the latest firmware (while on the 4.21 downgrader cfw).
Kinda frustrated, gonna see what I can and can't do while I'm stuck on this shiz and try and downgrade later.
Zombiekillah is my hero.