Well, my experience is that you can update OS anytime from any old version but the copied Map disks may or may not work. I have 2005-4.8is with MKIV. I updated my OS from v19 or so to v32 without any problem. I downloaded v32 using the links here at xoutpost. I was still using original 2004 map disk with this v32 with no issues. Then I got myself a copy from eBay for the 2011 maps and it never worked. I even tried 2011 copy from a friend but my MKIV didn't accept. Finally, i got myself the original 2011 map disks and everything is working like a charm.

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2005-4.8is