You should know I don't put much stock into outside validation. I don't shun it *who says no to praise?*, I just don't depend on it. One way I've found to know if I've grown as a writer, is to read some of my older work.
Compare and contrast. It's a very simple process. Open up a story you haven't looked at in a while. May be one of the first stories you wrote. It doesn't have to be completed, just earlier work.
Below I will provide a list of possible reactions that let you know you may have grown as a writer:
1. If there is a God why didn't he smite me for writing this dreck?
2. Fork. Eye. Gouge. Please.
3. What? What!?
4. I must have been drunk when I wrote this.
5. I sent this out to publishers?
6. No wonder I drove my CP up the wall.
7. I didn't write this, I couldn't have written this.
I could continue, but I think you get my drift. I was moving some old files onto another computer. I was feeling nostalgic and read my first book. Let's just say by the end of the first page I needed a glass of wine. I also realized that even on the days it feels like I'm getting nowhere, I have grown. No longer do I try to imitate Nora Roberts when I write. Okay, badly imitate Nora Roberts. I've come a very, very long way.
How far have you come?