Pressurized irrigation networks have improved water use efficiency, but deterministic sizing does not anticipate off-design performance. The pressure reliability index (IF), Todini resilience index (IR), and supplied demand ratio (IQ) were evaluated in two gravity-fed branched networks, Tuncarta (Ecuador) and ARJ-42 (Spain), combining operation (on-demand and rotation), modeling approaches (demand-driven analysis, DDA, and pressure-driven analysis, PDA), and two uncertainty scenarios: stress testing and Monte Carlo simulation. Rotation operation was fully reliable under design conditions but lost reliability at over-demands of 5% (ARJ-42) and 10% (Tuncarta). Under random opening, median reliability was 0.90 in Tuncarta (one-third simultaneity, exceeding the design value) and 1.00 in ARJ-42 (design simultaneity). Under pressure deficits, DDA overestimated delivered flow by up to 45% (Tuncarta) and 83% (ARJ-42) and produced negative resilience values without physical meaning. Both networks exhibited three deterioration zones and, with all hydrants open, supplied 69% and 55% of their reference flow rates. The framework supports design validation and expansion planning.