Updating inventory levels with CSV import

Is it possible to adjust a Product’s inventory levels relative to its current levels (for example, +10 would add 10 more available units to the current available units) through the Inventory CSV import?

Scenario: We receive units of a new Product and publish it. A few units sell. We receive more units and want to make those available in Shopify.

The Inventory CSV import appears to override the available number for a Product, instead of add to it. This means we need to know how many units have sold, which means we need to export data from Shopify into our inventory system.

I am not sure about CSV import, but you can make inventory changes with Excel formulas using a spreadsheet app for Shopify.

You can add a column with the newly arrived inventory and add it to the current inventory.

The inventory is synced automatically with Shopify.