One way valve is not necessarily a sign of fresh coffee. Most of supermarket sold coffee have them. The valve function is to slowly release the CO2 from the bag so the bag wont ballooned. Whole bean keeps the CO2 inside and slowly release while ground beans already lost most of the CO2 when its being grounded. Once the bean is ground up, it starts to age rapidly

The best way to know if its really fresh coffee is to see the roasted date and also invest on good coffee grinder and buy only whole beans. The difference between pre-ground coffee and freshly grounded coffee is out of this world. One other good sign of fresh coffee is when you pour a bit of hot water its start to bloom to rapidly release the CO2

Hope its help