The general rule is increasing temperature by 10C roughly doubles the rate of chemical reactions. https://www.ddltesting.com/package-testing/shelf-life-testin...

Though in practice it’s more complicated. Basically, make predictions based on accelerated testing and then validate them in real time tests. So, if things hold up at 3 and 6 months real time you can probably trust them over longer timeframes.

Not OP, but this is the same way lightbulb or hard drive manufacturers can claim "greater than 50,000 hours of operation". Instead of testing for over a decade, they test many samples over a shorter time duration, and then they extrapolate. Like any other extrapolation, these estimates have their caveats. But for biological reagents, something like an exponential decay is often considered reasonable.

Accelerated studies. Usually you test stability for shorter periods of time under harsher conditions. It’s not perfect, but if your product is fine at 50C for 2 months, it’ll probably be fine refrigerated for 12 months.

Assume that the reaction rate (shelf life) versus temperature relationship is described by the Arrhenius equation or some other model; perform experiments at elevated temperatures, and extrapolate to lower temperatures.