I'm not gonna comment on the SD thing, I don't know either way. But in terms of Def Jam...consider the deal again. 10 mil to Nas. Promo handled by the label, NOT taken from the advance. Two labels involved in profits. 1 platinum album. 2 gold albums. Labels get (at best) around 62% of sales after you take out distribution, samples/publishing, the artist cut, etc. You don't need a finance degree to see that doesn't add up to a profit for Def Jam or Sony.
By 2010, Nas was feuding with Def Jam and upset about only being offered 200k for Lost Tapes 2. If his run was as successful as you say, why was he so upset AFTER releasing multiple albums that sold decent to well? I thought Nas overall did well on Def Jam. The problem (from the label perspective) was that he was given a deal he would have deserved at one point in his career, but a deal that was too generous to the artist at that time, given the type of music he was making.
The thing about labels is that a small handful of artists keep the lights on. Everything else is kind of just...there. Whether you're a modest success or a modest loss, at the end of the day the label will let you ride out your contract as long as they have a Lady Gaga or Beyonce or Drake or Hov to make everything work. Not to mention catalog/legacy sales (Whitney Houston, Michael Jackson, etc). Nobody lost their job because of the Nas deal. But you don't give a 10mil deal to someone unless you expect them to sell multi platinum albums and have hits. That's not what happened. And as a label guy who worked in finance, that's all I'm looking at. The other stuff is whatever.