Finally, I did it. Successfully updated my PS3 to Rogero 4.21CFW v1.09.
Model: CECH-2508B (datecode:0D) (base firmware downgrade possible:3.50)
Updated from Kmeaw 3.55 without dehashing as never downgraded
(I have changed firmwares before from kmeaw 3.55 -> rebug 3.55.2 -> Cobra CFW -> kmeaw 3.55) apparently changing firmwares while on 3.55 does not affect the syscon check and you can upgrade without dehashing.
All games work fine from internal. Delete game data once. For external, enable bd-mirror and games which give black screen require EBOOT resign or latest update to work. Borderlands 2 and Risen 2... YAY!!!!! Thank You to
... and to all the beta testers of this CFW version..!!!
PS: Any updates from 3.60+ work. They did not be of 4.21 only...