If a musicologist can recognize a sample, then either (A) royalties need to be paid, or (B) court costs do ;) It happens a lot in commercial music; often the sample is modified enough that it can't be recognized, but I happen to know a couple of folks who make a fine living identifying copyrighted samples, tracking down the violators and extracting substantial royalty fees from them. Sometimes it takes years -- but believe me, that doesn't stop the lawsuits.