Do Altera timing models cover worst-case voltage?

Although the timing models used by the Quartus® II software are named using the nominal Vcc voltage, the models actually cover worst-case voltage. For example, the Stratix® IV GX device Slow 900mV 85C timing model covers worst-case voltage corresponding to the minimum supported Vcc operating conditions, which is 870 mV. Similarly the Stratix IV GX Fast 900mV 0C timing models covers worst-case voltage corresponding to maximum supported Vcc operating conditions, which is 930 mV. For further details on timing models used by the Quartus II software, refer to Guaranteeing Silicon Performance with FPGA Timing Models (PDF).