Take for example the concept of "Property is theft." Is property being stolen or theft being stolen? Is it the antecedent concept that is being stolen or the concept that's being used? The following description by Branden seems to suggest that theft is the concept that is being stolen.
However, the answer to this question suggests that it is the antecedent concept that is stolen.
UPDATE #1 One answer states that the questioner misunderstood the antecedent concept as being base on the structure in a proposition rather than the hierarchical relations of concepts. The questioner did not.
The questioner was confused by this statement in the linked question
Let re-label the concept "social justice" to be BLAH. The questioner is fully aware that justice is the antecedent concept to the concept of BLAH. When the questioner read the sentence of "That expression "steals" the concept of justice", he interpreted that as the concept of justice was being stolen, not the concept of BLAH. If the answerer intends to communicate that it is the concept of BLAH that is being stolen, or rather, the BLAH-justice portion of the compound concept was being stolen, then that could be made more clear. :)
There is a huge confusion in this question over the meaning of "antecedent concept." The explanation of concept-stealing uses "antecedent concept" to refer to the hierarchical relation of concepts, while the questioner is using "antecedent concept" to refer to the structure of a proposition of the form "S is P," in which "S" is designated as the "antecedent" and "P" is designated as the "consequent." The issue that defines concept-stealing is the contextual dependence of the stolen concept on other "antecedent" concepts which the stolen concept uses implicitly and relies on, while denying and undercutting them. In the hierarchical usage of "antecedent," we are referring to what had to be known first, before a later concept could be formed and have meaning. In this usage, "antecedent" does not necessarily refer to which term happens to come first in the order of terms in a proposition or expression.
In a proposition of the form "S is P," either term can be a stolen concept. In "property is theft," the stolen concept is theft, because the proposition denies "property" apart from theft, but "theft" has no meaning without the concept of "property." Conversely, "I do not exist" uses "I" while denying that which makes "I" possible, namely, the existence of whoever is asserting the proposition in reference to himself. "I" is a stolen concept in that usage, since a conscious being of some kind has to exist in order to assert that proposition. (If the meaning is clarified and qualified, as in "I existed once, but no longer," engraved on a tombstone, for example, then the hierarchy of concepts can be preserved and concept-stealing avoided.)
(Technically, the "antecedent" and "consequent" in a proposition most often refer to propositions of the form, "If P then Q." But "All P is Q" is equivalent to the proposition, "If x is P, then x is Q.")
Update: "Smuggled" Concepts
A substantial update to the question provides considerable additional context from which to understand more clearly what the questioner found confusing in the explanations and discussions of the "stolen concept" fallacy. On checking the excerpts on that topic in The Ayn Rand Lexicon, I found the following:
When I checked OPAR, I found a very clear statement on p. 136:
[The fallacy of the "stolen concept"] consists in using a higher-level concept while denying or ignoring its hierarchical roots, i.e., one or more of the earlier concepts on which it logically depends. This is the intellectual equivalent of standing on the fortieth floor of a skyscraper while dynamiting the first thirty-nine. The higher level concept ... is termed "stolen," because the individual involved has no logical right to use it. He is an epistemological parasite; he seizes, without understanding, a term created by other men who did observe the necessary hierarchical structure.
I believe this explains perfectly why "theft" is a stolen concept in the proposition, "property is theft." The application to "social justice" is a little more difficult (for me, at least). The expression, "social justice," uses the concept "justice" in a context that cuts justice off from its proper epistemological roots, so I maintain that one can describe "justice" as a stolen concept in that usage. It probably would also be valid (if I understand the Objectivist view correctly) to refer to "social justice" as a stolen expression. It's certainly also true that "justice" is being "smuggled" into the expression "social justice," and "smuggling" could be taken to mean "stealing" it from its proper context in order to misuse it.
I hope that clarifies any confusion by me and/or others about the specific issue of what is being stolen. I've always found it easier to understand the fallacy as a whole (i.e., using terms cut off from their roots) than to worry too much about what is being "stolen" from what. But the OPAR description makes a lot of sense to me, after having studied it more closely.