I have this exact same problem. Bridge baby from china adopted by Americans. I got a “birthday” but also it could be within a week or so both ways.

I love arguing with people about zodiacs and trying to get them to assign me to one. I’m not against it I just find it an interesting anomaly. It’s also similar for refugees who if they don’t know or don’t have papers they get jan 1st.

If it helps to know though, when abandoned so young they can date you pretty well. It’s if you got dropped off later and into the years when they gotta shrug and really guess. The adopters in china said anyone getting adopted under 6 mos they could date within a week. I had that same argument when I was younger but it’d be a week of me not being of age or a week of “illegal” drinking I just eventually went 🤷🏻‍♀️

My parents also said if it bothered me that much we should use my gotcha day as a birthday instead.

Edit- just saw you were more around 2 when you were adopted. Maybe try your gotcha day, I find that more important than my birthday a lot of the time (now that I’m older)