As the headline states, does it go far back? The relevance of my question is to the sad state of the modern collection of Omega these days when they have neglected to produce one for the newest diver 300.

 

The two different sizes for the same model seamaster diver started with the "pre-Bond" Seamaster in the late eighties I think.
When the SMP 300 was introduced Omega offered a third, ladies size watch without the helium escape valve that both the fullsize and midsize had.

 

Omega is going to make whatever sells. If people are only buying big watches, why would they make a midsize?

IMHO. I'll add though, if a nice midsized (like 38mm) was available for the new SMP, I would have bought it. Instead, I bought the 42mm which is a bit much for me.