Hey James, how you doing?
If I'm not wrong, I believe Sampras doesn't have a lifetime contract with Wilson, so I don't think he wants to unnecessarily advertise Wilson through the stencil. The last time I heard, he was using VS gut in the mains and Luxilon in the crosses on his Ncode.
As you may know, he had both the Wilson AND Babolat stencils in his racquet during his professional days:
What I'm curious is: Does Sampras still have a contract with Babolat because of the Babolat stencil he's using nowadays? Otherwise, why would he have the Babolat stencil on his Ncode other than for contract/advertising purposes?