As I tell people frequently, Ellisons are a customer of S2. They are bound by what S2 put in place as criteria for sales. If you are buying everything you should have to perform Shellac services to the CND and S2 standard, then you should have no problem in proving that with recent invoices of pùrchase from Ellisons.
Ellisons are not running the Certification process, it will be S2 so you would be smart to also register with S2 as well to take advantage of the salon /business locator and the Certification process. Most people have accounts at both as Ellisons do not sell of the CND products as you probably know. HTH