I don’t think I’ve ever seen anyone misuse the word “greaves” in English. It always means armor for the lower legs. The correct translation for “quijote” is “cuisse.”
Heinlein didn’t invent these. Footnotes of this type were prevalent in magazine sf of the '30s. And the footnotes were not the worst thing about this book in any case.
And Heinlein deserves some credit for know it was bad and not trying to get it published when he was alive. So not lost, more hidden.