On the Executive Summary, the customers metric is de-duped on a daily basis, meaning we are showing unique customer counts on the daily granularity. However, when rowed up to a weekly/monthly etc. view, what’s shown is the sum of all daily customer counts within that week/mo etc.
For example, lets say my 1st order is 1/1, then i repurchase on 1/2 1/3, 1/4. When rolled up to weekly, I’d be counted as 4 customers (1 distinct customer daily on 4 different days summed over days of the week).The logic here is that when you roll up to the year, the customers metric is not saying how many unique customers bought for that year, it's how many customers bought total, only being sure that it was unique on daily granularity.To get fully de-duped (unique to any date granularity) customer counts, the Customers Deep Dives (New Customer and Last Order Analysis) are the best places to look. These pages dynamically de-dupe customers on whatever date granularity you’re looking at, meaning you’ll be getting the true count of unique customers within the date aggregation.