I also believed that shoulder length is my terminal length because even at my longest my hair was only an inch or two past my shoulders. Now that I think about it, though, my hair was a mess. I was doing all the wrong things. Not washing often enough, wearing it out every day, constant manipulation, daily heat, improper moisture/protein, balance, you name it.
So I think to myself, "If my hair was in bad shape before and I was at shoulder length, how long will it grow if I am doing all the right things?" I am back at shoulder length now. I guess I get the average .5" a month, so I figure that I should be at APL by December.
My hair is definitely healthier, and while the growth may not be so out of this world (it's hard to notice because I have layers), I have retained the growth that I have had. I can not advocate enough the importance of protective styling at this length. I wore my hair up in french roll everyday for the past four months and my ends have thanked me. Also, what has helped is DCing at every wash. Having a low manipulation hairstyle, moisturizing daily and stretching relaxers help tremendously. Also not obsessing over my length aided me. It was hard to wear that damned french roll every day, but it was a means to an end. When I finally revealed my hair, people were asking if I had a hair piece. I have been kind of bad lately by wearing my hair down, but I have started back to protective styling. I wear it clipped in a low ponytail. It's not cute, but it's worth it.