Think mine said SBC too - for S model, B boxer, C cup but I think dealer just wrote that as his own informal acronym on the receipt. Not aware of different Boxer Cup models.
Here's a weird question for SBX owners - did you get a lug wrench to remove the rear wheel with your tool kit? I don't think it's included with the SBX (although I pointed it out to the dealer on pick up and he threw one in). That must explain the price difference
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Congrats, you'll love it - I do.