So on this domain I support, they have a KMS host which is set up correctly for Office 2013 and there is no problem with it, but recently additional licenses for Office 2013 were purchased.
On the volume licensing website, it shows Office 2013 and the number of licenses has increased as a result of the new purchase, so that is correct as well. Under license keys though there is another MAK and KMS key.
What do I do with the new KMS key? Anything? Clearly Microsoft have got the correct licensing total. Never been in a situation before where licenses were purchased incrementally like this.