It would seem to be that accuracy of their work was not properly valued by their previous supervisors. If you can't offer a proper reward for accurate work with recognition, promotions and raises in pay, or other incentives, you may have to resort to demonstrating that there can be negative consequences. Discuss the situation with your boss.
Perhaps you can try a recognition aspect first. Many employees respond equally as well to recognition and respect as they do to a raise in pay. At least in the short term. A competitive scenario can also work. A 15 minute monthly recognition assembly? Or offer a paid dinner to the person that reaches the highest level of production (units produced/number of errors), or any other incentive of your choice.
Failure to be recognised has a surprisingly high place on the list of things that make employees think about leaving. Number 2. The #1 spot, realising they reached a dead end. Money is usually #3, if it enters the picture at all. Most of us just want to be appreciated for our work and that can take many forms. Often it only has to be a word from their supervisor at the right time. When they do good work, sometimes no matter how small, take a second and tell them how that one tiny thing helped you out.
You might also try turning the tables on them. If both do the same type of work, then make each one correct the errors of the other. It's a bit on the negative side, but it can be effective. Keep your eye on how that works, or doesn't. It can go off track, if it gets too serious.
Generally we all want to contribute to the team effort and if you make the success of the team dependent on the work of each member, the team automatically applies the necessary heat or oil, in one form or another, exactly where its needed to get the best results for the team. It's the loners that are responsible for only their own work alone that get caught in the "I don't care" attitude trap that will bring everyone down.
To see if someone really understands an instruction, or learned a lesson, ask them to explain to you, in their own words, what you just told or taught them.
A black swan to a turkey is a white swan to the butcher.