The threads over at Netkas indicate that the refurb machines are way our in left field and that there's a lot of manual manipulation required to get the updater to put the 2,1 FW on them.
Yes, I'm considering changing processors, so I want to have a way to make my machine recognize them if the FW I have now does not.
I'm not at that machine right now, but I recall that the System Profiler noted that it was manufactured in 2008. I suppose that was when it was refurbished, and I got it shortly after that as a paid replacement for the DP G5 that I had that would never work correctly for the three years I had it.