finally, "papers" is being acknowledged rather than "newspapers" for diarios. But I didn´t expect because in earlier lessons this was not the case.
Yes, but it is less commonly used for newspapers. Most are printed daily so we don't bother to say it, although we might say "the daily newspaper" we usually just say "the newspaper". I wonder if it would accept "the daily national newspapers", but as it would be uncommon, I doubt it.
But would ''los papeles nacionales'' be understood to mean the national NEWSpapers, they way it would be understood in English? I've never heard anyone use ''papeles'' for newspapers, but in English it would be understood to mean newspapers if you just said, ''the papers.''