Student confused about the power flow problem

[AzureMight]

Hello, I'm not a EE student, but I have taken an interest in the power flow problem, especially because I was assigned a case study.
After hours of reading the book written by Alexandra von Meier, I believe I have obtained a very high level picture of what the power flow problem, but there are still a few things that obscure me. Please correct if there are any things wrong with what I'm saying.

First of all, I was confused for a long time by the fact that a few variables are called knowns, when they are blatantly not known at all.
In particular, the real power generated at PV buses is NOT known in reality, it's just a rough estimate, that's why there is a slack bus to begin with: The slack bus is supposed to correct the errors.
The real power supply is known only in terms for the analysis. It is a specified variable.
Does it mean that when analysing a real world scenario, what is really given as input for data is only the load values? The inputs for generators are in reality parameters subject to fine tuning, which is done to obtain several results for comparisons, right?

 

[rhatcher]

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