I agree, the title is misleading.
I don't remember seeing a successful downgrade post here either.
What this thread is really about is a modified lv2diag.self that partially works on 3.55. The original file will simply exit to xmb (i believe) whilst this one will initiate the downgrade process, but stop when it gets to coreos, leaving a soft-brick in the process. You should know that this will not and will likely never work on a ps3 that was on 3.50 or higher from factory, this may never be possible.
What is needed to complete this is a modified firmware to downgrade to, or "upgrade" to.
STOP! Before you ask questions... READ the first post! RTFFP = Read The F*cking First Post
Yes, A 3.55 "jb" (cfw) is available, no >3.55 "jb" or cfw yet.
Yes, A 3.55 downgrade is available. But not to lower than stock firmware! (What it came with)
No >3.55 downgrade is out there yet.