There is one official mock exam which will be the expected grade for the final. It is the official one the school/college puts forward to the examining board as part of the course, and the one they fall back on if you don't attend or need a remark etc.
The others are just practice papers. I did 4 practice papers and 1 mock before my final exam last year.
The official mock is done under exam conditions sometimes in the place you will take the exam or in the class room, it just depends on the school/college.