That might be the number for the backbox only.Thanks for your quick reply.
I'm planning to keep my resonator, so I will need to cut it somewhere to get it fitted but that's fine to me.
I just got the information that the number stamped on the exhaust I'm looking at is 5Q5253611AM, which is the same as the ST Cupra Carbon version (with resonator), I'm happy with the soundclips of that car on Youtube as that should be the same for my Cupra.
Of course it is possible to cut the resonator from your original exhaust to put to the new one and then add a few sleeves/brackets to hold it all together.