Performance period - general info

I have not been able to find out much info on perf periods, so I have a few questions. If I have missed an area that provides good general info, please point me in the right direction: -Confused where they are documented, some credit forms have them, some do not. -There is also boxes on one of the Pf forms requesting Earliest start date and Latest end date - what are the consequences / intent of that info? - what does it affect? -Can your performance period be prior to your date of registration? -Are the forms linked together in any way to coordinate the required time period overlap, etc Thanks