More or less, by using the seating depth of a manual without knowing the details of the reamer and chamber they used to run that data, you should be okay in terms of trusting that you won't get a pressure that is too high. Most of the major manufacturers use conservative approaches to what they publish in their manuals. This philosophy includes giving some description of what they use to test in terms of example rifles or test bbls.
Once you read enough and start down your road of learning to develop loads, you will get the hang of what the shared data really means and what you should expect to get. I tell beginners to start with a 5.56, .308, or .30-06 for the sole purpose of getting their learning curve under the benefit of a huge body of standardized test beds and pet loads. Once they survive their learning curve, they have the experience to go off into less charted territory with much higher confidence and safety.
Never get complacent, you are born with your fingers and your eyes, make sure you keep them there...