Headcanon of some sort.
When Lyra meets a version of her parents - be they dark, alternate, the original, a bit mental, too early, don’t know her, too late in their time stream or anything really that means they don’t know her - she won’t come out and say ‘Mum!’ or ‘Dad!’, but will pretend she doesn’t know them. Well, she’ll know who they are, but won’t express who they are to her. If that makes sense.
This really, really kills her inside. Because as much as she tries to cover it up with her naturally happy personality and constant trips to foreign lands she will always miss her parents desperately. And that will hurt for her until she finds them again. Or they find her, if the case may be.