I think the problem here is that you're trying to map {ngIq} into a single English word or concept.
I disagree. It's fairly clear to me why the English translations are what they are. There may be ambiguity in that we don't fully know how to extend the use of {ngIq} *beyond* the examples, but I don't think the examples taken together are ambiguous.
Because {ngIq} always deals with a collection of things. If it meant "They kill a single person", what happens to the others?
Same.
It means something like "with one move out of a collection of moves". The surrounding context makes it clear the translation should be "in a single move" rather than "in each move".
Based on the canon examples, if you make a single statement with {ngIq veng}, it means "in each city (out of a collection of cities)". If you make a series of (structurally identical) statements with {ngIq veng}, you're explicitly listing what's done "in a single city" (going through each city in the collection). The ambiguity is in what happens if you use it in another way (e.g., how similar do the list of sentences have to be for the "single one" meaning?).
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De'vID