After adoption

When we adopted our daughter, I had this apparently crazy idea that we were going to keep in touch with her birthparents...well birthmother at least. Her mom is very young and although we never formally met, I've seen her (and I think her me) when I was dropping off for a visit and in court, and we had a really great communication through writing letters during visits. I thought for sure that she would want to keep in touch after the adoption. When it was time for mom's final visit, I wrote her a long letter talking about what we hope to give our daughter and asking her if there was anything in particular that she hoped for her that we could instill...such as culture, languages, sports, activites etc... Birthmom never showed up for the final visit for reasons unknown to me, but I could guess it was just too hard for her. It was a complete end to the relationship. Is it weird that I'm feeling a loss here? I have seen her in town a few times, but wouldn't dare approach her because I feel that would be invading her privacy, but it kills me to know that she is that close and there is zero contact. I created an email account and gave her and her birth father the address, and neither have contacted us. It's only been about a year and a half since the adoption was final and I'm sure they will be dealing with this for many years to come, but I can't help but feel like there is something missing. Have any of you registered for the Adoption Registry? What is the process and how much information do you have to give? I want contact, but since I know much of both parent's history, would not way to give personal information. How does this work?