after looking into it more carefully i realized that -B just means "bulk", it's a different ordering part number for the same motherboard. the website i linked probably just had an editing mistake anyway, thankfully, supermicro did at least one thing completely correctly and it is "put a few components on the PCB so that the flash can be powered up and accessed with a SOIC clip". desktop SKUs often don't have this and it's really annoying. this is the chip i'm expecting and, unlike the other Macronix device, this one has accurate SFDP