is the plastic region really plastic?

[Chazef]

I'm assuming that plastic means deformations are permanent, because that's what I've been taught. Anyway I was wondering if the non-linear section of a stress/strain graph is really entirely plastic, because when you determine the permanent strain of a material after fracture, it's less than the strain of the plastic region (sometimes), which suggests that some of the strain from the plastic region was actually not permanent and therefore there is some elasticity in the plastic region. Pic related.

Also, I've made a formula for determining permanent strain, which is 'strain at failure' - ('Stress at failure' / 'Young's Modulus'). Is this correct, or do you just determine the strain of the plastic region of the graph.

thanks in advance