Ancient Neologisms
Some neologisms seem like they've been around forever. Some people even believe that they've been around and describe their grandparents using them and so on, in some kind of Mandela Effect but they are nonetheless neologisms. I don't have a comprehensive list, obviously, but here are a couple.
Sweet Summer Child
Most commonly in "Oh you sweet summer child". The use of it to disparagingly mean "innocent and naïve" is decidedly from G.R.R Martin's A Song of Ice and Fire series.
Yes, James Staunton Babcock used the phrase in The West Wind, but it is obvious that in describing the wind he's not referring to its innocence or naïveté. The west wind is genuinely and sincerely a sweet child of summer, described as formed of light and air. It's really more of an ode to the wind itself. No sense of innocence exists.
Yes, Mary Whitaker used the phrase in The Prisoner, but it is obvious there that the "fragrant breeze" is a result of the Summer and that it is sincerely sweet and mild. The sense it is used there is to set the scene for the pleasant climes and surroundings.
There are supposedly other references where it is used by Fredrika Bremer, but I cannot find the original source, and considering the obvious misunderstanding of the use of the phrase in the other two, it doesn't strike me with confidence.
This is obviously the result of some kind of full-text search as opposed to any comprehension of the phrase, its use, and subsequent use as a disparaging phrase. Mere textual coincidence as opposed to commonality of meaning.
This is somewhat reinforced by the fact that if you search Google Books you'll get a lot of references, none of which actually are used in this style.
In conclusion, the use of "sweet summer child" as following the writing of A Song of Ice and Fire and referencing the in-universe multi-year sense of seasons with Summer being relatively pleasant and Winter being treacherously cold is a post-GRRM phenomenon, no matter how many n-grams have been identified before. The fact that no references use it in the GRRM style reinforce that this use of the phrase is novel in that book.
