From what i recall, there were two changes from 2003 to 2004. When I was asking a friend about the differences, we were talking about the mark 4 10x. I would assume the changes affected the whole line, but I don't know that for sure.
1)They changed the coating on the scope. I was told there was not a huge difference.
2)They made the thread on the eyepiece not as fine so that adjustments could be made with fewer turns. Personall I couldn't care too much about this since I only set the thing when i first put the scope on my rifle, so I don't really care how many turns it takes. Plus you may have to turn it less, but the adjustment ability isn't as fine so it is sort of a trade-off
I don't ever remember hearing anyone complaining about 2003 and earlier scopes, and I don't hear anyone complaining since they made the modifications. (What a helpful comment that was)
J