Many of the resource books will tell you the date of the piece if you know the name. My favorite research book on Sarah Conventry jewelry is " Emmons and Sarah Coventry Jewelry Fashion Show - Deborah A. Robinson."
This is a video that I put together on YouTube which shows 13 pieces of Sarah Coventry jewelry from the middle of the last century with design name and date of manufacture.
Most Sarah Coventry jewelry designs are quite collectible today.
For a great range of Sarah Coventry jewelry, please visit Vintage Jewelry Lane. Sarah Coventry jewelry is one of the specialties of my site.