You are right.  Cost is updated from invoice if goods receipt has been done first. But not if Invoice is posted first with FIFO.  No entry in Stock valuation in these cases.

Even worse with foreign currency.  

We have set up Anglosaxen accounting, and then manually reconcile the difference in the stock input account to a COGS account (price difference account).   Accounting will about correct. But this is not ideal process. To much manual work.

But there is also an obvious process that will solve this: Register Prepayment to the vendor if you need to register invoice before goods receipt.  The register final invoice, after goods receipt.  And then reconcile the the two postings.

There is an app for this that install the prepayment option in purchase similar to prepayment in sales.

https://apps.odoo.com/apps/modules/17.0/purchase_vendorbill_advance

 When using Standard Price, any difference between the purchase price and the standard cost gets posted to the Price Difference Account. However, with FIFO or Average Costing, Odoo doesn't directly use the Price Difference Account because the actual cost of goods sold is updated based on the incoming goods' prices.