OK, I now have the additional SPN’s added to AD that I mentioned in my post and a listing returns:
Registered ServicePrincipalNames for CN=[servername],OU=Member Servers,DC=[domain],DC=biz:
So when I now try to log into SQL server using spdata.ep-dev.[domain].biz/EPDev and Windows Authentication, all is well and I can connect to the server.
When I try moving the databases I will need to move this SPN to the new SQL Cluster, and it should work there as well.