FAA checkrides are now governed by FAA Airman Certification Standards (ACS). RideReady is 100% FAA ACS compatible. We cover the material that you are expected to know per the ACS. The ACS leaves a fair bit of latitude for the examiner to cover a wide range of topics and materials - and we help you be ready.
As far as the question of "do I need to know everything?" goes, the answer is "definitely no! however..." No examiner expects you to know everything. RideReady is written such that if a person knew everything that is in there, he/she would likely be an amazingly outstanding applicant. A small percentage of the questions included in each test prep (especially the earlier stage ones, such as Private and Recreational Pilot) are beyond what is normally expected of applicants. We nevertheless include a few such questions to allow you to potentially be truly impressive.
So, don't worry if you don't know all of the answers. Your goal is really to be functionally literate in the subject matter. "I don't know, but I know where to look that up" is a perfectly good answer for some checkride oral questions - but just don't use it too often! Your primary goal is to demonstrate to the examiner that you have competence in the material and that you have good, safety-minded judgment. The examiner is not expecting you to know everything, but don't take the oral lightly - people probably fail the oral exam portions of their checkride just about as often as they fail in flight tasks. You want to be over prepared rather than under prepared.