IMHO Spencerian is not a base for copperplate. Spencerian was designed by Platt Rogers Spencer as a running hand and is a lovely hand for everyday penmanship.
He based it on organic shapes and it is very rhythmic.
Yes, it has fewer shades than copperplate, but the shapes are quite different.
Rather than ovals, the basic shape is more of a teardrop.
Exemplars that simply drop the shades from copperplate are not true to Spencerian.
The IAMPETH website is a good place to find the original Spencerian exemplars.
This is just one link - there are more.
https://www.iampeth.com/pdf/new-spencerian-compendium