It seems to happen quite often, actually. Many of us have either never been at a healthy weight or not for many, many years so it's really hard to know exactly what that number will look like once you reach it.
Personally, I was 140lbs once before in my life but it was in high school, before having a kid, and before lifting so my body has changed a lot since then! I have a hard time imagining that I'd want to go below that but I might decide to go above it.
Mostly once I hit a healthy BMI I'll take it one step at a time.