Large price difference for same in-demand model (Nautilus?) made in different years?

[FrançoisCzapek]

for certain Patek models like steel Nautilus models, why does year of manufacture seem to matter? I’ve seen for example a 2020 steel Nautilus sell for substantially higher than an identical 2010 watch, assuming condition and servicing is the same.

Is there any rule of thumb for this? What do you watch out for if you are, for example, considering a gray market buy of such a model that was made over several years? Do the watches from earlier in a model’s run somehow lose value but not the ones made later in the run?