Hey,

I don't think there is a clear answer to your intial question because some clients come into therapy and open up straight away and tell the therapist everything about themselves, some open up a little at a time and others perhaps take one step forward and two steps back, so it can take a therapist varying times to get to 'know' clients.
They try their best to understand their clients but they are human and can make mistakes or misjudgements, just like you or I.

Often clients can struggle to even know themselves fully so its impossible to expect a therapist to know us completely.

To help your therapist and yourself you can tell them when they say something that is wrong or upsets you and in that way you help them know you better

all the best