I don't think its possible to mix the motherboard up. You pretty much need to use the same model anyway if they did. If you don't have the previous Nand dump before you sent it in for reflow, not sure how you would check.
What model PS3 do you have ? What makes you think they switched it?
Check this guide: ps3devwiki.com/wiki/Flash#cISD1_-_Section_1
Thanks for the reply. The system was a virgin launch CECHB01 on 3.50 and failed their re-flow 2x's (the 1% fail in their claimed 99% success rate).
To make a long story short my system chassis had damage both top and bottom and came back in a different chassis. When I opened it to verify their work (it needs a reball now according to them) I found that what they told me didn't jive with what I saw.
Not to mention that some screws were missing but marked with a marker. They tried to convince me that the screws were missing when they opened the virgin console and the chassis was mine because the SN on the back matched the work order. Blah, blah, blah... something is fishy here.
I'd rather try to identify the /type/ of board they sent you back, not the serial number. If they did bang up your original mobo it's only right that they get you another matching one. "Matching" being the key word here.
Look for the white lettering "COK-00x" (where x can be 1 or 2) on the board. Should you not find it, try to check what motherboard they slapped in (A list is here: ps3devwiki.com/wiki/Motherboards)
This reminds me of a shop some years ago that would mod your console, but would switch the parts with worn out ones. They would not let you see what they do to the consoles. So one day I took a PSOne to them, but made a tiny mark on the lens before that. When the guy brought it back, he immediately made the comment that I knew what was going on.