It feels weird that you are so adamant about saying "but this wouldn't work if it was a fake name!". Everyone knows this? What's your point? As if it's an issue, and people are using their new name in job interviews and official paperwork before it's legally changed.

No one here is saying your employer can't push back if the name you give them doesnt show up in governmental systems. Who are you having this convo with?

I'm sure you mean well but it felt you were trying to be purposefully obtuse.