Open Welsh Championship in mid-1920s

[OnTheRoad]

My mother Sadie Mitchell and her brother Aelwyn were on the stage when they were young (from 1921 to 1935, with a few breaks in between) and I have found the following advertisement for them in The Era in May 1927 plus there are other ads stating similar:

THE MAGNET TWINS – Wales’ Premier Juveniles. Winner of Open Welsh Championship for four successive years. In dainty song scenas. Remarkable success everywhere. 

I have tried researching the Open Welsh Championships and can only find golf back in the 1920s and in the present day there is ballroom dancing. Does anyone know specifically what the OWC were for back then and are there any records that I could look into?

As always, all suggestions and information will be very gratefully received .

Cherryl