Thanks guys. Apple Support told me it means they are used, even after we both agreed Argos are an authorised seller.
I then went to the store explaining this, they was shocked and would replace them. However, no stock... I drove 15 miles to another and they switched them there. Before leaving, I checked the serial number and this time it said warranty expires May 05th 2021, less time than the original pair.
Me and the manager checked the other 6 in stock and all said a date in May.
Seems they aren’t used, they’re brand new. Just that the dates are all wrong.
The Apple advisor never said anything about sending evidence of purchase date to correct the warranty start date, causing me a lot of hassle, time and petrol. ?