These Oher's own words from his 2011 book, I Beat the Odds: From Homelessness, to The Blind Side, and Beyond.
https://books.google.com/books?id=ErNPEAAAQBAJ&pg=PA169&lpg=PA169&dq="It+kind+of+felt+like+a+formality,+as+I’d+been+a+part+of+the+family+for+more+than+a+year+at+that+point.+Since+I+was+already+over+the+age+of+eighteen+and+considered+an+adult+by+the+state+of+Tennessee,+Sean+and+Leigh+Anne+would+be+named+as+my+“legal+conservators.”+They+explained+to+me+that+it+means+pretty+much+the+exact+same+thing+as+“adoptive+parents,”+but+that+the+laws+were+just+written+in+a+way+that+took+my+age+into+account.+Honestly,+I+didn’t+care+what+it+was+called.+I+was+just+happy+that+no+one+could+argue+that+we+weren’t+legally+what+we+already+knew+was+real:+We+were+a+family."&source=bl&ots=51PvhRADLx&sig=ACfU3U06GPt-SBMjVtuEMhbX_1KWo9zEcw&hl=en&sa=X&ved=2ahUKEwjMqc2koeGAAxWYkGoFHVxVBe4Q6AF6BAgwEAM#v=onepage&q="It kind of felt like a formality%2C as I’d been a part of the family for more than a year at that point. Since I was already over the age of eighteen and considered an adult by the state of Tennessee%2C Sean and Leigh Anne would be named as my “legal conservators.” They explained to me that it means pretty much the exact same thing as “adoptive parents%2C” but that the laws were just written in a way that took my age into account. Honestly%2C I didn’t care what it was called. I was just happy that no one could argue that we weren’t legally what we already knew was real%3A We were a family."&f=false
Given Oher's quotes from a book he wrote 12 years ago, any claim by him that he only recently discovered he was adopted is bullshit.