The trouble with physical books is that we need to have a copy to hand when we want to reread it or refer to it. This morning, I referred to Poul Anderson's
David Falkayn:
Star Trader when composing
The Basis. Later,
David Falkayn... seemed to have disappeared. In fact, it was on the shelf where it should have been but the title on the spine is so faded that I did not notice it.
I have:
"Margin of Profit," unrevised, in Anderson's Un-Man and other novellas (New York, 1962) and, revised, in his The Earth Book Of Stormgate (New York, 1978) and The Van Rijn Method (Riverdale, NY, 2009);
"Territory" in Anderson's Trader To The Stars (St. Albans, 1975) and his David Falkayn: Star Trader (Riverdale, NY, 2010).
"Territory" quotes an explanatory passage from "Margin of Profit." In the unrevised "Margin...," that passage includes the sentence:
"Automation made manufacturing cheap, and the cost of energy nose-dived when the proton converter was invented."
-"Margin of Profit" IN Un-Man and other novellas, pp. 103-129 AT p. 110.
In the revised text, that sentence becomes two:
"Automation and the mineral wealth of the Solar System made the manufacture of most goods cheap. The cost of energy nosedived when small, clean, simple fusion units became available."
-"Margin of Profit" IN The Earth Book Of Stormgate, pp. 68-100 AT pp. 77.
Thus, fusion units replace proton converters.
Of necessity, "Territory" in Trader To The Stars quotes the unrevised Margin... because that text had not been revised yet. However, "Territory" in David Falkayn... also quotes the unrevised version with proton converters instead of fusion units.
(And, if I am not a Poul Anderson scholar yet, then I am training to be one.)