But my SC's - which is what they legally are - spend 50% (minimum but that's another thread...) of their lives living in my home, in which I am a parent. So it is perfectly right for me to have a parental title. I cook for them, clean, wash and buy their clothes, do school runs, take them on outings, put them to bed, help them with every aspect of their lives- just like my DH does for my DC's.
It is entirely right that I have a parental title as I perform every function of being a parent- I'm just not Mum or Dad, I’m a step parent.
It's accurate, and fair.
That's not the same as someone the kids have barely met, not yet a stable relationship with their Mum or Dad, not living with them etc, however, stable, married, living with, and functioning as a parent (albeit on a slightly lower level than Mum/Dad) it only makes sense they have a parental role.
It's no different to granddad etc, there is a parental role involved, but still not dad.