For your second question, my understanding is that the carrier is responsible to returning you home if you do not have the required documentation for entry, hence all the stories of people being denied boarding at their departure because of information in the system.

I would assume trying to keep up with all the information on all entries of all countries relative to every other country in one place must be on the level of herding Adderall affected kittens while drunk, wearing a blindfold and listening to polka music played on bagpipes.