I came across this website that has a list of meanings for kosmos, which include under 8b, "of believers only." See: https://mikejeshurun.wordpress.com/2013/10/12/a-w-pink-on-the-world-of-john-316/

I see two problems here; the first minor, the second major:

First, assuming the definition is correct, why would anyone cite "1 Cor 4:9" as an example of kosmos referring to believers? That doesn't make sense to me.

Second, and more important, what other reliable and scholarly language resource has "of believers only" as a definition for kosmos, and citing John 3:16?

Thanks!