I had a win xp machine with office 2003. I copied out the nk2 file and copied it over to new win 7 machine with office 2013. I ran the outlook.exe /importnk2 command, it renames the nk2 to nk2.old (so I put it in the right place in the win 7 machine), but when I do a new email, there's no autocomplete recommendations.
I ran the outlook.exe /cleanautocompletecache command to clean out 2013 before starting again with the importnk2. I used the nk2edit app to see that there are lots of items in that nk2 I brought over.