there are emulation test suites. the fact you throw out 'there should be auditing' without acknowledging the literal _years_ of documentation and research leads me to believe you know nothing on the topic, rather just want complain on hacker news about something you have no involvement in.

MAME literally scans the dies to read the chips and understand their logic. FPGAs faithfully recreate this as well. and no, you can still run a 8bit micro on whatever display you want. Projects like dolphin and BSNES documented the hell out of everything they do with a goal of accuracy in mind.