Here's a link to the manual:

 

< ADMIN NOTE: Broken link has been removed from this post by Dell>

 

Under the display section it shows:

Vertical

+15°/–30° (WXGA)
±50° (WSXGA+)

I don't see a WXGA+ for this system, but I do see a WSXGA+...

I think your dealer meant WSXGA+ ?  that shows to have the +-50 degrees.