[not_a_bijection]

You can do better. X86 has both "op [mem], reg" and "op reg, [mem]" variants of most instructions, where "[mem]" can be a register too. So you have two ways to encode "xor eax, eax", differing by which of the operands is in the "possible memory operand" slot, the source or the destination.

[mpeg]

This one would be a fun challenge in a ctf, or maybe more appropriate for a puzzle hunt – most people would look at the dissassembly and not at the actual bytes and completely miss the binary encoding

[zzo38computer]

Some disassembly listings will also include the actual bytes (there are multiple reasons why you will want this).