Amazon nowhere says that the invoices appear to be fake. Amazon’s reply is: “Illegible or didn't match records” - Illegible can mean anything, for example older as 365 days, as stated in the article. The second part about records not matching is just company speak to make it look like the vendor is to blame. It’s intentionally vague. My wife worked as a vendor manager at Amazon and she never checked any manufacturer receipts/had a way to check them.
Inventory receipt management very much sounds like something that Amazon should have as part of its interface (presuming it's not already). Sellers should be able to upload receipts/purchase orders to their accounts at any time.
It's just good sense to have all of these images available at all time, regardless of selling platform.