> This is very interesting. Could this mean that we could say {puq mob} for "only child"?

I think it would be highly contextual. When talking about the constitution of a family, talking about the {puq mob} might well refer to an only child. However, if you were to say something like {wa' puqDaj mob ngeHta' joH'a'}, I think it could just as well be interpreted as "The LORD sent one of his children, and no one else."

I don't think there is sufficient canonical backing to make any far-reaching conclusions, but the one canonical discussion of {X mob} that I'm aware of concerns the story where ghunchu'wI' ordered {bIQ neH} at a restaurant, and Marc Okrand suggested that what he really wanted was {bIQ mob}:

https://www.kli.org/tlhIngan-Hol/2012/July/msg00127.html

In this case, it would not make sense to interpret {X mob} as "the only existing X", as that would mean ordering the only water the restaurant had.

//loghaD