If you could open your old names.nsf files, open it in LotusNotes, select every contacts (and site documents if any), copy to clipboard.
Then create a new NAMES.NSF or use an other one and paste all you docs in.
If you don’t have any addresses in your new contact book yet, you can rename that file to oldnames.nsf and put the old one in its place, as names.nsf. Only do this with Notes closed!! Then when you reopen, it will be the default address book again.