Arguements Over a Critical Point

I agree that dating probably will not work on living creatures, but when I was doing research for a paper I had to do I found several sites that explained a situation that I thought put dating to question. Scientist took the carcass of an animal that they knew had been dead for about a month but when they used the dating techniques the result said the carcass was hundreds of years old. Scientist use this dating technique to date things that noone knows the age but when used to date a known age it failed. Granted the science behind the dating techniques may make sense to some but how do they actually prove it? I feel the technique does have holes, but the scientist are unable to accept this because like I said previously they can not prove the technique is always accurate because they do not know the actual age of the object being tested; so how can they compare the result with the actual answer. I was always under the assumption that science was built on proof not assumption.***Sorry I could not find the site I found most of this information.