You don’t seem to understand the prefix trick at all.

In English, I can say, “I gave the apple to you,” or I can say, “I gave you the apple.” That’s really the core of the prefix trick in Klingon. In either case, the apple is the direct object of the verb “gave” and “you" is the indirect object. If you just go by strict rules of English grammar and extract “I gave you…” out of the sentence, you’d tend to assume that “you" is the direct object, but seeing the whole sentence, you know better.

The grammars of English and Klingon in this example are completely different.

First let's look at the English. There are two ways we can say this:

I gave the apple to you.

Here, the apple is the direct object. There is no indirect object. Instead, we have a preposition, to, which has an object, you. The you is not the indirect object of the verb gave.

I gave you the apple.

Here, the apple remains the direct object, but you is now the indirect object. In English, the indirect object comes between the verb and the direct object.

Now for Klingon. Here, we also have two ways to say this:

SoHvaD 'epIl naH vInoppu'.

Here, 'epIl naH is the object (never mind direct or indirect; it's the "object"). SoHvaD is the beneficiary. Semantically, these words play the same roles as the direct and indirect objects, respectively, in English, but in Klingon the roles are "object" and "beneficiary."

'epIl naH qanobpu'.

Here, 'epIl naH remains the object (again, never mind worrying about direct or indirect; it's the "object"), but the beneficary has disappeared. Instead, we get the prefix trick, using a prefix that does not agree with the object. This tells us that the prefix trick is being used, and it tells us that the indirect object of the sentence, what would normally be the beneficiary, is SoH.

{SoHvaD chab vInob. chab qanob.}

The prefix {qa-} suggests that “you" is the direct object (when “you” is actually the indirect object), similar to the examples in English.

The word that comes before the verb is the "object," not the "direct object." Sometimes you can distinguish the English role of direct or indirect object for the Klingon "object," but to Klingon, it's just an "object."

For one thing, plurality doesn’t tend to play into the prefix trick. The prefix trick typically uses “person” to reveal itself. First or second person subject and an indicated second or first person direct object shown in the prefix, but an explicit noun in the 3rd person in the word-order position of direct object. That’s the classic prefix trick.

Except our definition of the prefix trick was expanded a couple of years ago. See the message the OP referenced. Specifically, if there's no possibility of confusion, third-person prefixes may also be used for the prefix trick. The given example is lujang for they answer him.

We were also told that the earlier revelation about the prefix trick, the one specifying first- and second-person object prefixes, was simplified for brevity.

The prefix says “I [verb] you” or “You [verb] me”, but there’s an extra unmarked noun before the verb jumping up and down, yelling, “I’m the real direct object!”

Explicit nouns are the actual objects; prefixes merely agree with objects. Assuming it's not an error, if the prefix doesn't agree with the object that's sitting right there, then it is agreeing with an unstated indirect object.

{loDnI’Daj vavDaj je ja’ qeylIS} is not an example of the prefix trick. It’s just a common Klingon grammatical error.

It is not an error. It is evidence that Klingon verbs take "objects" as arguments, not "direct objects." You have never let go of this desperate idea that Klingon verb arguments are strictly split between direct and indirect objects. They're not. Direct and indirect object are not syntactic roles in Klingon; they are syntactic roles in English that are sometimes used to describe things that are happening semantically in Klingon. The relevant Klingon syntactic roles in this topic are "object" and "beneficiary."

-- 
SuStel
http://trimboli.name