The sentences are set up to cover all of the main grammar constructions for the specific grammar point. For some there are a lot so they only get covered 1-2 ways (plus the one or two in the writeup about the grammar point). For others, there is just one way it is constructed.
If there is a special rules like な adjective + だ + から(because) we include sentences that force the special constructions and catch attempted answers where you forget the だ, giving you a warning about the rule.
For the order in which you are quizzed on sentences, we go through the list of sentences progressively and only give you ones you haven’t seen until you have covered them all before you see the same sentence a second time.
Hope that helps answer your question!