The classic boot-sector aliasing trick (0x0000:0x7C00 and 0x07C0:0x0000 are the same physical byte) shows up throughout real GRUB and syslinux source code, and the BP-defaults-to-SS-not-DS quirk you note here is a genuine, well-documented gotcha that has bitten generations of assembly programmers writing stack-frame access code. 4096 different segment:offset pairs can name a single physical address, which is exactly why disassemblers must normalize addresses before comparing them.