I have lost 2 cores on my 965BE. I hadn't noticed, but it was pointed out to me via Futuremark and 3Dmark11 and SpikeSoprano from Overclockers Club forums.
Back in 2010 you had a thread about this issue and one guy said he reseated the CPU and it fixed the problem.
I'm going to do that and hope for the best.
I had flashed the BIOS from 1101 to 1301 and after five minutes of checking, I still had missing cores.
I was about to reinstall windows when I noticed that windows task manager had the four boxes back. The Flash fixed it and brought the AWOL cores home.