Target cannot limit workers compensation rights nor limit the financial responsibilities that entails if they are found at fault. The 12 week thing is a smokescreen where they reevaluate your condition. They cannot legally push you out by a set deadline but trust me they will find ways to do it aka attendence, metrics etc.
The 12 weeks is instituted so they are not in a situation where you claim that you cannot do any particular task, for any department, in perpetuity. In some states you can file an injury claim a year after the adjoining incident and within five years if secondary complications arise from the initial injury.
I had an injury through a different company that got messed around with for three years with various delaying tactics on their part. I had one team member who actually sued Target to get a settlement because they were giving her the run around.
If Target does fully fund their workers compensation, penny for penny, rather than through a direct insurance carrier, they are still held to state worker compensation laws. They are required to have workers compensation in all but in a couple of states. Target will just be more vigorous in denying everything but worker comp adjuncts can step in. That is why it is important when you first get hurt to go to a doctor of your preference or that is impartial. The doctors in worker comp cases are some of the scummiest around.
Ironically enough, with worker comp doctors being so disingenuous it is not unusual for companies to fully finance their workers comp division. They not only need to worry about workers being dishonest about their injuries but with doctors who only have loyalty to the worker comp insurance companies themselves. There is a reason why work injury clinics churn out so much volume. It was not unusual even with my concerns about my injury where my doctor's visit were less than two minutes long. I could have cut out a ton of needless visits and we could have actually try and solve the injury I had and not treat it like a "boo boo". It was ridiculous as not only was the company not interested in helping alleviate my injury, but also the workers comp insurance company and the doctors' that "I had to visit" to keep me in compliance.