We know that Regression and many statistical techniques are used to predict and estimate things in the real population on basis of our sample data.

What if we have the whole population at our hand. If you are a researcher working in some university and you've got the whole results/information of students. Can't we use our multivariate data to model the phenomena at that university? so we can use the model for prediction.

The population of a university changes quickly too. The elements (students of the population) are changing every semester.

I don't know how best should we use the data we've got.