As Klahanie has already said, 'Cerro Potosi' does not die back in the winter. The lower growth is quite woody by the end of the season, whereas 'Amistad' is firm but still soft

well they are both perennial for starters.
as said Amistad is herbaceous. that means in cold weather it dies down totally [soggy mass of stems etc] and grows again from below soil level in the spring.

Shrubby means that towards the end of the summer it makes secondary growth that is hardened by lignin and that makes it shrubby/woody. Leaves may be lost but many leaves may be kept, depending on the severity of the weather. In the spring new growth starts from buds along the stems.

Thank you Klahanie, Andrew and Eileen ... all helpful. I’m sure my S. Amistad is supposed to die back, but in the greenhouse it is thriving with plenty of new growth! But the ones still in the ground I will mulch (I’ve taken cuttings). I appreciate your expertise 🙂.