I left out an important point in my prior point when I was talking about no matter how the word is translated.
What I should have said there is that I think Bailey ended up calling it concept instead of preconcept because what Diogenes Laertius is describing (at least it seems to me) is clearly conceptual reasoning, which I gather you and I both think is very distinct from prolepsis.
Which means that I am siding with DeWitt's analysis of this section from Diogenes Laertius, and I think Diogenes Laertius is wrong in describing this process as prolepetic.
DeWitt sees conflict between Diogenes Laertius' understanding of prolepsis:
QuoteAnd we could not look for the object of our search, unless we have first known it. For instance, we ask, ‘Is that standing yonder a horse or a cow?’ To do this we must know by means of a concept the shape of horse and of cow. Otherwise we could not have named them, unless we previously knew their appearance by means of a concept.
.... vs Velleius' (Cicero's) explanation of prolepsis in "On The Nature of The Gods":
Quote“Anyone pondering on the baseless and irrational character of these doctrines ought to regard Epicurus with reverence, and to rank him as one of the very gods about whom we are inquiring. For he alone perceived, first, that the gods exist, because nature herself has imprinted a conception of them on the minds of all mankind. For what nation or what tribe of men is there but possesses untaught some ‘preconception’ of the gods? Such notions Epicurus designates by the word prolepsis, that is, a sort of preconceived mental picture of a thing, without which nothing can be understood or investigated or discussed. The force and value of this argument we learn in that work of genius, Epicurus's Rule or Standard of Judgment.
.... and DeWitt thinks Velleius' explanation is more consistent with Epicurus' use of the term,
So I'm going at present with the view that what DL is explaining is not prolepsis but ordinary conceptual reasoning, involving comparing one opinion against another. In contrast what Velleius is explaining is something "nature-imprinted" and "without which nothing can be understood or investigated or discussed." This latter statement seems to me to describe something that deserves to be considered as "canonical."
I would distinguish that from: "I've seen five cows and horses now I have a picture in my mind to which I am going to attach the name 'cow' and 'horse' (or any number of other words in other languages). Certainly that's related to how the mind words, and I would say that prolepsis is involved in even getting the mind working, but by the time you are talking about "cows" and "horses," and we apply those words when we see other animals, you are in my view in the realm of comparing opinions against each other, and i think we agree that opinions are not preconceptions.