He might be basing it off a thread like this, where 'mmc info' gives some things that say 512.
https://community.nxp.com/thread/377766
Yeah, I would have expected the write address to have needed to be at 0x41000, that's why I'd love to know how his device is working now, or if there were any Other steps he took.
I suppose i should ask of we are certain those addresses are still correct for 8th gen devices, I haven't looked at that.