So I've been scratching my head over how to restore my Blu-ray playback, and I'd been unsuccessful until today. I thought that the only 2 Blu-Rays I'd watched on my PS3 were Apocalypto and Transformers. I'd been messing around with the MKB files and running them through DRLgen to create the .bin files, without any success.
I then stumbled across th BD Data Utility on the XMB, on here it showed details of all the Blu-Ray films I had watched, along with the dates. This reminded me that I had watched 2012 also (a copy I borrowed, so didn't have the original disc), and that it was the most recent film I had watched. I managed to find the generated DRL file online, along with the knowledge that it was level 16 security.
All I did was to create a DRL from a Bluray I had (Transformers) using the MKB_RO.inf to create the 2 .bin files. I then opened these up in a hex editor and replaced the HEX with the DRL info from 2012 I found on the net. I put these in the "PS3bluray" folder on my USB, inserted into the PS3, ran DRL copy and after restarting my PS3, BLU-Ray was restored!
Just to confirm, my hard drive was formatted when I downgraded, and when I restored my data from a back up it kept the data on the "BD Data info" on the XMB.
Basically this info can help re jog your memory over what discs have been played, along with the dates. I hope this helps anyone in a similar position I was In.