Nevada lets you add UM/UIM limits only where you paid a separate premium, and pays UIM as damages above the other driver's limits
Nevada's rules are in NRS 687B.145 (offer of UM and UIM, how UIM pays and the stacking rule) and 690B.020 (UM required unless rejected). Minimum limits are in 485.185, the fault rule in 41.141 and the deadline in 11.190.
Read how stacked and single-limit coverage differ in Nevada, check what section 687B.145 says, or see how Nevada UM and UIM work.