I am a writer and composer with (unfortunately) a fair amount of experience enforcing copyrights and keeping publishers honest.
Generally speaking, you can only recover actual damages (ie, "lost revenues") unless you can prove fraudelent intent, which is NOT the case as the publisher admitted/claimed it was a "mistake."
Probably you could get an accounting of sales and the publisher then pays you that. If they're making sales you might not want to alienate them as this could possibly be an on-going revenue stream.
My suggestion is to keep a close rein on your lawyer or their "billable hours" may eat up all of your income. Lawsuits are the anuity gift to attorneys.
This is interesting, please keep us posted.