But it's all tied to time. So, for example, at any point in time there are latest stable packages that should only depend on other latest stable packages, there

But it's all tied to time. So, for example, at any point in time there are latest stable packages that should only depend on other latest stable packages, there is no point doing other combinations, hence no combinatorial explosion. And if it doesn't work with the latest stable dependency, it will never work with it anyway and has to be linked with previous stable branch of that dependency, still the only version though and no combinatorial explosion. No matter how you look at it, time constraints possible combinations to a small number.