[78-L] Approximating 78s age by physical characteristics

[David London]

On 04/03/13 03:51, Michael Biel wrote:
>
> Victor Red Seals were mostly single-sided until 1923, but few pop
> records were single sided after 1911 or 12.
>

I have some early Zonophones labelled "The Twin" which look old enough 
to be from early the 1900's.  Were they among the first double sided?  
When did they start using both sides?