Why? This was an administration error. The fact that the decree was acted upon incorrectly doesn't invalidate the decree itself, which says "These two people should get divorced". If the firm needs an additional decree so that they can divorce the right people (e.g. because the original decree has been executed and is no longer valid), then that's what they can ask the judge for.

Otherwise, the victims in this case have the UK tort system available to them to seek a remedy for any damages they may have suffered. They can also just get re-married and ask the firm to cover those associated costs.