I watched the mini-sode again this morning. I got the impression that the sisters elixir didn't 'replicate' the regeneration, it just amplified it...made it less random I believe they said, so 8 could choose who he needed to become. I'm not sure that that's the re numbering outer that Moffat has planned. It's too weak.
It was also said that he was dead already meaning he missed his window to regenerate (so it can't count as one of his) and that the Sisters had taken Timelord technology and perfected it. So this was NOT one of his regenerations, it was an artificial regeneration added after death.
-Nick