I tell no one, as this is in accordance with my children's wishes. It's on a need to know only basis.
So far that's been medical reasons only. I don't tell school as they don't need to know -there are issues but they don't need to know they are adoption related.
There is always someone in the family who is eg has green eyes, is , sporty, has red hair etc. if not, I would just say
" you know, it's a mystery to us as none of us are musical. She gets her good looks from me of course "
If a child was with with bio grandparents, I woudl just say " she's visiting relatives " . No one actually wants to ask and hear the explanation that it's your second cousins twice removed or someone who is not actually a relative but used to live next door to your mother.
I think you are taking these questions too seriously and believing that they need an " honest " answer. Most people are just making polite conversation.
" Did you breast feed her ? " doesn't need a explanation of the biology and politics of adoption lactation. It needs "no she was bottle fed " .
Even if they persists and ask "Why? " you just say " medical reasons " or " for a lot of reasons " .
The questioner doesn't actually want to know about your BF experience. They want to talk about THEIRS.
Ditto birth stories . You can just say " oh, it's a long and complicated story, I'm sure you don't want to hear it /I never talk about it /it's a long time ago " < roll eyes >
If you keep smiling and keep saying the same thing over and over again in slightly different way,most people will not persist, I promise you.if they do,they are just being rude and you are perfectly entitled to be more direct with them
" mum, I know that you want me to tell you about Dds birth family , but I've already explained to you that's her information and we are not allowed to discuss it with you .i find it very upsetting that you keep asking me about it and I'd like you to stop . We are not going to change our minds about this "