This was my thought too you have been watching too many episodes of CSI to think that the lab is going to say "nope the oil you gave us is a different blend then the stuff that you got out of the crankcase".
Even if for a second they were able to determine it there would be contamination form your crankcase of the oil that was in there before, making it even less likely to be definitive.
Now lets say the lab works miracles and says the oil samples provided by YOU are different. What then?? If you confront the dealership do you think they are going to admit they overfilled it? If I were the service manager I would simply say how the hel* do I know where you got the oil from you could have bought two types and now your going to try to blame us? Or are you going to break into the dealership after hours and draw an oil sample from their bulk tank to be analyzed too?? LOL
Forget the whole lab thing, and just confront the service manager with the issues you had POST service and see what they are willing to do.
I had a small shop recently install tires on my bike, I picked the bike up rode it home and then the next morning to work. I went to go to the store on brake and I hear a clunk and a strange feeling when applying front brake. same issue the never tightened the caliper bolts back on. The one bolt had worke3d completely out but a reflector bracket kept it on the bike and the other was about 3/4 ways out. I tightened it all up, (it was a SUnday) I callede the shop monday the owner was away so i Called Tuesday told him what happened and I would be later that day. I went in they checked everything and torqued it, then he then "compensated" me and apologized profusely. He also thanked me for bringing it to his attention so he could deal with the tech involved, (obviously he wasn't pleased as it is him who would have been liable had I crashed, and he acknowledged it was a SERIOUS error for the tech.
I was satisfied and that is why the story and the shops name never appeared on GTAM..lol
Never saw an episode of CSI in my life, porn just gets in the way of quality television. I'm going to BMW North America and present my findings to see what they have to say about it. I think the company doesn't need any shady business to boost their bottom line.