Harmony Test

Had my blood drawn at 10 weeks 2 days, and got my results back a week later. They said I was having a boy. (Which I'm fine with) but, I have read numerous stories about them being wrong when the mother has had previous boy pregnancies and it can detect DNA from them. I have had 2 boys already, one is 2 and the other is 1. Wondering if anybody has heard of this? Or know anyone or themselves experienced a situation like this?