I just canned some myself yesterday. You say you slightly precooked which means while it was in the canner, you finished cooking off the grease. In the olden days people would put there meat in crocks and seal it with some sort of fat on top to keep out the oxygen and preserve the meat longer. You should be ok but there is a chance that the fat turns rancid which is one of the reasons that the USDA don't recommend canning this way. They prefer all fat drained and fill jars with some sort of liquid. The way I do mine is cook it all the way thru so I am cooking off as much grease as possible. Then I just use a spotted spoon when I fill my jars. I do not add liquid. I think it changes the texture and also the taste too much. Wipe rim with paper towel ripped in vinegar, lid, ring, canner.
