The Mazda Dealership that carried out the first two services on my brand new 2016 MX5 ND1 was started up by a Vauxhall Dealer. Their large Vauxhall Dealership being in a different Town than the Mazda Dealership.
For those services they used a Vauxhall Oil (deemed from the Part No on the Invoices). I believe the oil used was Vauxhall Dexos2 ACEA C3 oil.
I understand C3 oils are mid SAPS and for Petrol and light duty Diesel Engines.
BlueAgave stated that C3 would be beneficial.
As far as I can see Mazda Supra oil containers do not give the API or ACEA, but if both are API SN then either should do for my mx5.
For both of our Mazda cars Mazda Engine oils are my personal preference. As John-M said
Mazda Customer services have given me the answer as to which Mazda Oil I should insist on for our Mazda SkyActive X.
Time to stop chasing my tail and regard my problem as solved.
Thanks to all who responded.