Avoiding all copyright material can be difficult. Some material widely assumed to be traditional is in fact copyright. Some folk song collectors claimed copyright of songs they had collected, sometimes to protect the source singers but probably in some cases for personal enrichment. Versions of traditional songs in circulation are often based on a particular recording by a professional singer, who may have compiled their version from a number of sources and own the copyright in their finished version. It's a minefield and requires careful research.

Trying to ensure that a recording contains only non-copyright material is therefore potentially risky, if it later turns out you have made a mistake. Obtaining a licence to allow you to use copyright material is straightforward and inexpensive, at least where it is registered with a collection agency such as MCPS or Harry Fox.