Again it is this word 'definition' which is causing problems

The 1954 Definition describes traditional music. Once this was synonymous with 'folk' but no longer - not for musicological reasons but because language has altered. It is meaningful to use this definition but only for certain purposes. These do not include prescribing what is allowed into a 'folk club'.

For at least half a century the meaning of 'folk' has widened to include a much broader range of music which defies definition but can usually be recognised. The fact that this is also called 'folk' may be confusing, and may be regrettable, but language has its own momentum. The term 'folk club', again by common usage, usually refers to this wider meaning. As long as what is performed is recognisable as 'folk' in this sense, calling it a 'folk club' is not inaccurate, even if it does not include traditional songs. Again, this may be regrettable but is how term is widely understood. Language again.

In practice clubs which want to focus on a narrower spectrum often specify this somewhere in their name or publicity material. Equally, clubs which want to put on an even wider range of music call themselves 'open mics' to distinguish themselves from 'folk clubs'.