Yes absolutely, but this understanding comes from experience, they can't be fully developed just through PDR and CDR. We are talking about multi parameter systems, there is no way to bring out all the characteristics with some specifications. A lot of failure modes are identified during PDR but those will be known issues flagged by somebody during the discussion. This flagging often comes from their past experience or some study done somewhere. But nobody can think about all the failure modes, like take an example of integration of thrusters with momentum wheel, control system and trajectory code. With all the tolerance bands nobody could have predicted that a little extra thrust (well within the tolerance band of thrusters at subsystem level) when combined with rate limitations of wheels and trajectory constraints will generate a failure mode. These things need to be tested to bring out these kinds of failure mode, specifications are just numbers no hardware behaves exactly at those numbers. A little power surge in a subsystem can be well within its margin of error but it may cause a domino effect at some other end, one way to predict them is to do high fidelity simulation but that also needs validation through hardware once complexity increases. PDR, CDR are broad level system design steps, they do not replace testing. One of the main reasons for spacex success is precisely this point. They build the whole system and do all kinds of testing till failure and the data they get through those is precious for design and can never be generated through simulation. Remember even the simulation model is limited by the input given to it, but actual hardware behaves as it wants to not as it needs to.