To be honest, the size discrepancy isn't exactly rare. 1TB HDDs show 931GB usable. 512GB will show less also. And due to it being an SSD, there will be space reserved for SSD operations, overprovisioning that is.
Better explained:
"1GB according to the disk manufacturers is equal to 1,000,000,000 bytes. According to how the operating system (and the rest of the computing world) calculates it, it's equal to 1,024 megabytes, which in turn are equal to 1,024 kilobytes, which are themselves equal to 1,024 bytes. So one GB as per the disk manufacturer is really 1,000,000,000 / (1,024 x 1,024 x 1,024) = .931GB as measured by everybody else. So a "500GB" disk has 500 x .931GB of storage, or 465GB."