Good question - mostly I guess no as they sometimes seem intent not to refill until other levels drop too.
Mostly this averages well enough. Yet for a few things - like tikka where ratios seem consistently wrong. As Britain's favourite curry, you'd expect a few extra jars of that in every box. Or Cumberland sausages up here in former Cumberland - just forget about whatever the other things in the box are. :)
Probably means going the other way that when they drop something there's a chance 1 of the 2 or 3 actually sold well.
They basically don't do this for perishables. And they don't seem to restock if there's still some on the shelf. I'm pretty sure they can't afford to waste 30% of a product!
Eg. the 30% of the box thats the flavour that no-one (at this shop) buys, goes off and is dumped, for every box.
Maybe the ratios are determined by their global sales, who knows. You would think that it would be advantageous for each shop to tweak its own ratios.