Revelation 4-21 doesn't have any red lettering at all, which correlates at least indirectly to the fact that a popular interpretation of Revelation reads this same section as future events. This interpretation is especially popular among those with premillennialist views, and many of those with premillennialist views focus extra on preserving a word-for-word, literal rendering of the text, which is the first two of the NASB's main goalsNASB's main goals. Therefore, because of the high popularity of this interpretation of Revelation and the link between those who support it with those who have strong sola Scriptura literalis values, I think it's fair to guess that the NASB translators might have had this particular interpretation of Revelation in mind. And if they did, they would have also viewed chapter 4 as a major transition in the book. Yet even if they held to a different one, most other interpretations view chapter 4 as at least some kind of major turning point (the μετα ταυτα makes it pretty clear). This correlation is indirect: if someone interpreted 4-21 as strictly future events, they would not necessarily come to the same conclusion as the NASB translators did in 4:1. Nevertheless, if they had held to this interpretation, I believe it would have guided their translation in 4:1.