The New Customer Analysis dashboard is only showing data for customers who were acquired within the selected date range -- this is not necessarily going to represent your entire customer base since if a customer was acquired before the selected date but repeat-purchased more recently, they would not be included in the New Customer Analysis data.
To get a more complete picture of your total customer counts, we recommend heading to the Customers - Last Order Analysis page -- this page will show all customers whose latest purchase happened within the time range, regardless of if it was an acquisition order or repeat.