There's no "allowed" defined for mistakes*...they're just a reality that most people will understand, depending on the specific circumstances of each. They're not going to be like "3 typos in the PS are fine, but 4 and they'll never be a doctor!"
*with the exception of the grade input section, where you are in fact allowed a specific number of errors in verification before they make you correct it yourself and re-submit at the back of the queue
Sent from my phone, I apologize for any typos or brevity.