Fake Oxycontin 80's? OC on one side, Nothing on the Other!?

My house is the "older teen/young adult" hang out spot because of my roommates 19 year old twin boys. My roommate is prescribed Oxycontin 80mg... and because of all the traffic, he counts his pills regularly... a known fact in our household. After taking his nightly dose my roommate told me it wasn't working, which promted us to check his bottle... the count came out right but I noticed that some of the pills looked different... they had the OC on one side, were the same size, but DID NOT have 80 on the other side. A fingerprint has been found on one of the pills and an investigation started. Does anyone know what is being used as a fake Oxycontin 80s? And has this become common practice? We have also been told that we were not "duped" that someone must have wanted "Brand-Name" Oxycontin and replaced them with Generic ones.... I have researched the drug and have found no similiar generic (same size, same color, just no 80)... My main question is... "Is there such a Generic" and if not, what do you think was ingested? Thanks in advance.