Relationships between Orders/Invoices

Hello all!

I've been pulling data from Unleashed, an inventory/sale management system, to report on our data.

The data model is broken up into a heap of different fields such as:

Sales Order, Sales Person, Sales Invoice, Product, etc.

I've built out relationships between all of them based off the Sales Order (as it's the core) but I'm having issues slicing the data as when I'm trying to report on the INVOICED sales (completed sales orders) it defaults to registering the invoice against the month the sales order was created, not when the invoice was created (at the close of sale). We could have months between an order being created and an invoice being sent out due to lead times on our product.

I've got the Sales order linked to a date table and something in there is where the problem is. I can't link the invoices to the date table as it would create ambiguity between the invoice and order fields.

Anyone got any idea here? I'm sure there's an easier way to solve this that i'm missing.