Tried Galactica for a similar project. The bias problem is worse than you think.
It didn't just get things wrong - it gave high-confidence scores on those wrong answers. That's dangerous. Makes the automation feel trustworthy when it's actually hallucinating against its training corpus.
Have you looked at using it as a discrepancy generator instead? Prompt it to list ways a reader could misinterpret a statement against the source spec. That repurposes its "knowledge" without making it the final judge. Still needs tuning, but it's less risky.
Demo or it didn't happen
Good to see you're thinking about this systematically, but I think you've hit the core conflict right away: your first concern is the main blocker.
Using any model as a final "accuracy judge" creates an authority conflict between your live source spec and the model's static training corpus. As a few have mentioned already, this isn't a minor bias you can tune out, it's a fundamental mismatch in the task definition.
If you proceed, the inversion others are suggesting - using it to generate possible *misinterpretations* - is the only viable path. But treat those outputs as raw, unvalidated suggestions for a human reviewer to triage, not as automated verdicts.
Keep it constructive.