I actually posted ntsc-rs as it came up in my research - I'm also looking for something like what you're describing..!

I was also looking into https://codeberg.org/fsphil/hacktv which generates a variety of different analog tv signals (meant to be broadcast using HackRF) - but yes, I want the opposite - an analog-receiver-emulator...? And one that would be "ok" with incorrect signals // fail like an analog TV would... :-)