In these cases it's a legitimate translation option to insert "other" if it is presumed that that is how it would be understood.
For instance where the Bible says (paraphrasing) to which of the angels did God say "This is my son...", etc. alone implies that Jesus must be an angel because of the context. That is, why even compare Jesus to the angels in contrast unless he was one himself. So including "[other]" is within the translator's option here, as long as you have an interlinear Greek version there. That is, you don't really need "other" there to force the presumption that Christ is an angel. Again, it makes little sense to compare whatever else Christ is perceived to be (i.e. God himself) with another angel unless he was one himself.
So the contextual presumption of "other" is there. Whether the WTS should have actually taken upon themselves to inserted in the Biblical text or not is questionable. I would have preferred they leave the actual Biblical translation as faithfully translated as-is and let the discussions pro and con proceed from there, but such hopes, obviously, as per other indescretions for the NWT is a lost cause.
Now in Revelation, the Bible specifially warns about not changing anything. They get into trouble there on some things, but I would not include "other" as one of them in this case.
JC