No-one has all the time needed to record everything available. Some kind of filter is required to avoid wasting time on material that differs from that desired. No doubt good singers were missed because of "mislabelling", no doubt some were included that "shouldn't" have been. Recorder A missed singer B for reason C - that may be sad but is not the end of the world. Other recorders will have missed other singers for other reasons.

The labels helped reduce the amount of wasted time and tape. They act as useful filters, but cannot be expected to be perfect, and neither should individuals.