MLM is right. According to MPEP, the practitioner is presumed authorized. So by filling the application, it is presumed that the practitioner is authorized to represent the inventor, as far are the practitioner follows the requirements.
OK. So that answers my first question ie, (why it's ok to file original app with no POA at all). Good to have this piece of the puzzle.
Even if there is no POA in the file, the office actions come to the corresponding address that is usually the practitioner's address. Especially when the customer number is liked to the practitioner's registration number, the proof of authority may not be required. But I am not sure. Does anybody know it?
Correspondence address is a completely separate issue from POA. It's not unheard for client to be corr. address but firm to be on the POA.
I've never heard that the presence of an attorney on the Customer Number is a presumption that the attorney has POA. POA links to Customer Number, and CN names the attorneys. But I don't see why CN without any POA has any effect at all. [You did specify "no POA in the file."]
But since we will need to obtain the declaration from the inventor anyway, it is safer and prudent to obtain the POA from the inventor as well. When after the assignment is recorded, the title of the application is transfered to the assignee. Even if now POI is filed, the USPTO will send the OA to the existing correspondance address.
As noted above, who receives the OA is irrelevant to the question of POA.
Without the assignee's authorization, the practitioner won't do work for them.
Don't understand "won't do work for assignee." You're saying that papers filed in the case by the attorney on the POA can't possibly be on behalf of the assignee, since the assignee hasn't authorized that attorney to do so?
So the practitioner is acting in a representative capacity until new POA is filed.
Representative of *who* ? Inventor or assignee?