re: If a CPA makes a mistake that results in interest and penalties from the IRS....

Was this for a business return? If you submitted a P&L and they didn’t net income from the rerun back to the P&L that’s something you may be able to challenge them on. If you just threw a bunch of 1099s at them piecemeal, and that income hadn’t been on a previous return, that’s a different story.

At the end of the day, it’s your return. You are basically asking them to prepare and file the schedules with taxing authorities.

Either way your best recourse would be finding a new CPA if you aren’t happy with this one.