I'm surprised that your dealer did not present you with proof that supagard was applied. Suggests that it was not :-(
I looked at their web site
http://www.supagard.co.uk/ but didn't see anything. Suggest that you try three things; 1. ask your dealer for written confirmation, 2, check that the dealer is an authorised supplier and 3, ask supagard if their suppliers should hand out some proof that the job was carried out, like s certificate.
good luck