Hi noreen.lodi!
Happy to address your question on assumption questions. In short, necessary assumption questions can indeed involve new information.
If you have PowerScore's course materials, I'd encourage you to review Lesson 5, which goes in depth into assumption questions. As discussed in that lesson (see, for example, page 5-2), one will encounter "Supporter" and "Defender" assumptions on the LSAT.
An answer choice falling into the "Supporter" class is one that fills in a missing piece or logical gap between the premises and the conclusion. These can often be easy to spot because there will be new information or a new variable introduced in the conclusion of the stimulus.
However, those falling into the "Defender" class can introduce new information. Effectively, they rule out or "protect" the argument from a possible source of attack or make something that could otherwise be a weakness into something that is no longer a threat.
To make up an example, suppose we have:
If it is raining outside, then I will drive my car to the store. It is raining outside, therefore I will drive my car to the store.
Overall, this reasoning seems pretty straightforward. A "Defender" assumption in this context could be something like "It is not the case that my car broke down," or even something bizarre, such as, "It is not the case that aliens destroyed the store." If either of these occurrences did take place, then the conclusion wouldn't follow that I will drive my car to the store--i.e., this assumes that my car works and that aliens do not destroy the store. A Defender assumption in the answer choices could rule out these possibilities--and in that case it'd be bringing in information not directly from the stimulus.