Hi Trevor,
It's likely that you do have 512GB. The probability is that the Brennan factory may have experienced a shortage of 480GB SSDs during the production phase and then substituted the next available SSD size, which was 512GB, in order to keep production rolling.
This is not a new occurence. Back in 2016 I ordered a 500GB B2 (this was an HDD model then). What was delivered to me was a 1TB model at no extra charge, so that was a nice benefit to me.
So good luck with your B2! It is a great device with many capabilities, depending on what you want to do with your music. I also purchase a BB1 about 8 months ago and this is another winner!
Regards,
Peter.