Delivery data is entered automatically if you use an ad server integration or linear distribution which you trigger by clicking on "update delivered quantity". You can also automate this and 7.6.7 Schedule "Update Delivery Data" for PreInvoices.
Additionally you always have the possibility to edit the quantity information at your pre-invoices manually.
Edit Pre-Invoices
Click Edit at the pre-invoice you want to change. Be careful with automatically filled in fields.
Edit Invoice Items
Navigate to your invoice items and click Edit at the item you want to edit.
Edit Quantity Information
Scroll down to Quantity Information and manually update the Delivered Quantity.
Quantity Information
If the checkbox Linear Distribution is checked, the values are calculated by the booked quantity and the duration (start and end date). If you uncheck this box the delivered quantity will be used. This checkbox defines if the amount is distributed linear or not. For instance, this is used selling fixed price products.