First
How can you determine whether the Engine Control Unit (ECU) currently in your vehicle is the factory installed one?
I called the local Volvo folks and was told that if it's a Bosch it is likely the OEM that was factory installed. They further indicated that there was no reliable way to ascertain whether the ECU module is the original one.
However, I have just taken notice of the fact that the unit currently installed has some yellow markings on the side, suggesting a salvage part, thus highly unlikely to be the original.
So isn't there a reliable way to find out what ECU unit was originally installed?

Second
I have two extra ECUs, all from Ebay, as a result of a mad attempt to deal with the nasty inspection process they have implemented here in Massachusetts.
How can I determine whether they came from a turbo, from an S70, or that they came from a 98 model, other than from the seller's say so?

Third
How can one determine whether these ECU modules are not infected with codes or defective?

Thanks to all for any input on these issues.