Are the Pantone color names mostly only used by Pantone? The names retailers use are mainly for marketing no?
In common parlance, like Angie says, I've heard 'cognac' used to refer to a whole range of mid-tone browns.
On the light end it if it gets really pastel it's no longer cognac and instead sand or camel or toffee. On the dark end it might be 'saddle' or 'luggage' (which overlap a bit with cognac I think) but when you get into really deep espresso or chocolate brown (think coffee bean color) it's definitely not cognac anymore.
Anyways that's what I've been assuming, wrongly or rightly, lol.