Despite its apparent durability, the dermis is subject to tearing. how might a person know that the dermis has been previously stretched and/or torn

Because stretch marks appear and are visible.

Stretch marks begin as red lines/tears in the skin and then fade into silvery-white scars which indicate that the dermis has been stretched.

These types of marks appear due to weight gain, weight loss, muscle gain, muscle loss, puberty, pregnancy, hormonal changes and illnesses. They are very normal and the majority of people have them, men and women.