Have you had a similar case where you're seeing a difference in the refund numbers on the Dashboard vs the Export you have just saved?

There's a pretty logical explanation for that. Namely, the Analytics Dashboard captures all line items individually, so if there are 500 items in total they will be shown on the Dashboard.

The data export has a column quantity. If there is a line item with a number bigger than 1, then the quantity will be incremented here. In this case, the export would show a total number of 499 items instead of 500, given that the quantity of that one will be 2.