Thanks, Ray.
There's no problem in doing that -- it doesn't matter that the v4 licence and sample sets had a previous owner (unless any relevant non-MDA sample set makers specifically disallow transferring licences in the licence agreements), and there's no need to identify the previous owner when upgrading.
The licences will currently be within the v4 dongle. During the sample set licence migration process the v4 dongle's contents will be erased and the equivalent v5+ licences deposited in the specified iLok account.