Hello again
Well that was good thinking about the music hall society, didn't know there was such a thing.
If you think Bertram and family lived in Luton then perhaps you could get to look at the electoral registers prior to 1932 when you believe he died , or even just before his wife died in 1960, that way you would find who also lived at their addresses, don't know how easy it is for you from where you hail from
Going back to Snowdrop, such a lovely name, perhaps she might have been taken in by a family if her mother was perhaps away or on stage somewhere away from home. I am trying to think of all possibilities here,
What about wills if you are able to search in London .
I do hope you have some joy in finding this family, frustrating isn't it
Louisa Maud