My evidence of progress looks pretty concrete from where I'm standing, although admittedly I'm unsure as to how we are defining concrete, maybe because I'm not really awake yet.
I see the evidence in how I am better able to manage in times of distress, in how I am rectifying maladaptive behaviors, how my relationships have improved, and how I have improved within those relationships.
But just in case I think I may be imagining my progress, there's always a bestie, my bf or my daughter who every so often comments on the positive changes they're witnessing, and that keeps me motivated to keep at it.