I was thought that periods should be counted by how many days you stay before you started another period e.g 28 days, 30 days, 33 days and 35 days. But not by the date it comes. Meaning Your period might start on the 6th of this month and the next 1 comes on the 12th of next months based on the length of your circle. Do you understand?

It depends on what you mean. Period can have /- days and note that they are some drugs or physical stress can affect your period timing