Yes, great finds and prompts, Barrie, including Hernani and rippleson stillicides.
Perhaps we should be wary, though, of treating everything as entirely consistent at every level. N wants the curious reader to look up Hardy's "Friends Beyond," so has to have K drop the clue, which if taken as a clue to K's character would suggest a knowledge of English poetry quite different from that implied in the blunder of K's gloss on "between Goldsworth and Wordsmith" ("a witty exchange of syllables invoking the two masters of the heroic couplet"), a blunder that clearly does have characterizing K as a key purpose. Perhaps K's knowledge and precise memory of Hardy's poem does much less to indicate his "real" past, or his present state of knowledge of English poetry, than to direct our attention elsewhere where N wants it directed.
In the gloss to "bounced a ball or swung a bat" the immediate purpose is to characterize K's comic inopportune self-promotion ("Frankly I too") and his acquaintance only with the British part of the Anglophone world ("soccer and cricket") and not with the customs of the world of the American poet he is supposed to be glossing: as a scholar, then, he is not quite as ignorant as Conmal as translator, although their limits lie in the same direction, and of course he has even graver psychological defects as a editor and annotator. His then listing the other sports, aristocratic, northern, or intimately and sweatily male, in the rest of that first sentence in the note to l. 130, rapidly takes the character-centered humor down other corridors in the Dedalian funhouse. His "Frankly I too never excelled," coming from such an egotist, need not disclose much about his "actual" skill level (while we entertain the idea of C's Zemblan past as true); it may be taken to imply, when that layer of “truth” starts to show another reality through it, only that K fantasizes that the future Charles the Beloved could repeatedly have engaged in soccer and cricket, sports that K with his reading in British fiction of the period of Prisoner of Zenda has mistakenly assumed to be standard across the Anglophone world. And as Barrie's comments make us realize (makes me realize and imagine for the first time), these two sports are comically and deliciously inappropriate for any "actual" Zembla.
As for "soccer": if VN played it at Cambridge as a college blue, he would hardly have thought of it as working-class in England (although he did play with factory hands in Germany
at the beginning of the 1930s). Since he didn't live in England after 1922, it's hardly surprising that he would not have picked up the 1950s-1960s British switch from “soccer” to “(association) football” in a book he wrote in 1961, especially in characterizing
someone like K whose exposure to English culture is indirect and dates back to the 1920s and 1930s.