USNews usage was more common, and you definitely could mix many of the formerly Communist states into the same category as Argentina and Mexico, although other Communist states were necessarily third-world hell-holes.
There's even a term "fourth world" that refers to hopelessly impoverished, or even "failed" states. Examples are Haiti, Bengla Desh, Eritrea, etc.
Wikipedia continues to be untrustworthy.
And you continue to be wrong.
Sec'ond World'
(sometimes l.c.) 1. the world's industrialized nations other than the U.S. and the U.S.S.R.
2. the Communist and socialist nations of the world. Cf. First World, Third World, Fourth World.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease
http://www.factmonster.com/ipd/A0642752.html
I've given three references Wikipedia, Univ of WI and Random House Dictionary that all agree the "second world" refers to the Communist States.
Please show me references that show otherwise.