I once heard a debate between Joseph Pearce and somebody else about whether Peter Jackson's Lord of the Rings films were any good, Pearce pro and the other guy con. At that time I hadn't really soured on Pearce yet (as I have since done in reading the intro of his work on the life of Shakespeare, in which I think he is a judgmental Anglo-triumphalist whose theory of authorialism [his term, which he calls a "philosophy"] shifts way too easily between big A and little a "author" in a way that paints literature as incarnating an author in a way only one person ever was incarnated because only one person ever was/is/will be worth incarnating ... as I say, I think his main goal in all of it is an Anglo-triumphalism combined with a "we conservatives know those liberals are going to hell" party). But even having not soured on him yet, I was still disappointed in him, although feeling kind of sympathetic at the time. The question at the moment was Tolkien on allegory and whether there was some type of healthy use of it, etc. etc., and Pearce was just kind of stumbled around trying to piece together some visual with his arm about good allegory being some succession of of hoops between the original and the allegory of it, rather than a single hoop between them or something, and it really wasn't working in my opinion. The formulation to which I myself have come is that, prescinding from the question of whether Tolkien hated all allegory (to which the answer is, I think, that he is all right with a limited use as long as it does not get mistaken for the core of "narrative art"; he openly admits in one of the letters that Tom Bombadil is an allegory of pre-fallen nature), what allegory is in its essence, whether major or minor, good or bad, is a copying of a narrative arc wholesale. To take a minor example, in that instance of it just mentioned in the parentheses, the instance of Bombadil, a small basic narrative is carried over completely: Bomdadil is prelapsarian nature and the ring is a problem when evil is in the world, so it's not prelapsarian, but rather postlapsarian; the proposal is made of having Bombadil take care of the ring and the answer is given that that won't work; this is an allegory of asking the theological question of whether prelapsarian nature can address the problems of sin after the fall, and the answer is "no." I would argue that every use of allegory that Tolkien would find problematic is one in which the whole plot is carried over as the main plot of the new work (Bombadil was a very on-the-side subplot; Jackson cut it out altogether).
So, cut to now, and I am rewatching Person of Interest for the who knows what time, two episodes at a time on my elliptical machine, and I just came across an episode in season 2 that has always bugged me, and it hit me that it's a corollary of the allegory thing that can help explain it. There is an aspect of PoI that I have always loved, which is that they do send ups of famous films, but in this episode, called "Proteus," they straight-up ripped off a more current and non-classic (I think). I used to think that it was the "classic" status that made the difference because people would recognize a classic as a tribute and not really confuse it, and I still think that that is a part of it, but I think this other part that is analogous to the allegory issue is more core. The classicss to which PoI paid homage are, for example, Rear Window, Les Miserable, Usual Suspects, It's a Wonderful Life, and Wings of Desire (I noticed a nice really small hat-tip to Speed in an episode too when a car's computer gets hacked and keeps the car going at 50 mph). The film I think they ripped off is the 2004 Taking Lives, with Angelina Jolie and Ethan Hawke, in which a serial killer takes on the identities of his victims. Allegory, and particularly the level at which Tolkien disliked it, is like the ripping off of Taking Lives in that the plot of that movie was the plot of the episode, straight-forward. In all the other cases, the setting was obviously a tribute to the classic: Reese in a wheelchair doing recon with a camera through an apartment window watching a guy digging in a garden and they think he may be getting ready to commit murder; a french law officer chases a thief who really has a heart of gold; a mastermind pretends to be the peon interviewed by cops after participation in a criminal activity (they had a nice hint that I missed on the first watching for Usual Suspects in the form of a comment on the coffee in a police station). But that is as far as it went: there was nobody buried in the garden and no wife in the picture and the super was innocent and the victim; the thief was not guilty turned law-abiding, but rather innocent and then forced into crime, and a mother, and the Interpol agent doesn't question his whole philosophy and drown himself in despair; and the mastermind is the only person involved on his end and he gets blown up at the end (and I think he was working for something other than keeping his own identity safe). The plot is not copied, just some setting or character element. The ripping of Taking Lives, though, was pretty much a straight copy: a serial killer is taking the identities of the people he kills, and they stop him.
Tolkien's use of allusions or borrowings of tropes, even plot tropes, is not for tribute, like PoI did, but rather simply to build what he is building, BUT it is similar to the classy send ups versus the ripping off. An instance is the use of the Numbers 20 striking of the rock that gets Moses barred from the promised land: A first born son (Boromir and Israel, often stated as the "first-born son of the Lord) complains, "why did you bring us to this desolate place, to die here?"; Moses/Gandalf is told to speak to a rock/stone(door) and strikes it instead in anger; there are 40 years/miles and on the other side Moses/Gandalf is prevented from entering the promised/golden land by striking the rock (in Gandalf's case, he had to strike again in the form of the rock bridge). Tolkien doesn't do a straight up allegory of the Numbers story, though. For one, Moses's not getting into the promised land does nothing but identify him with the first generation, who are also barred from entering because, at the outset of the 40years, they failed to trust God to protect them if they would enter on the report of the two spies (Joshua and Caleb), but Gandalf's forfeiture by falling actually helps his friends go to the golden land by escaping. And in Tolkien, there is a powerful threat (the balrog) that is totally missing from Numbers, which is simply about the failings of Moses in relation to the failings of the first generation. There is a common element of the issue of a less than perfect leader making a mistake, but the whole narrative of what flows out of that is different. Tolkien's tale is not a simple allegory of the tale of Moses, like PoI ripping off Taking Lives, but rather the trope of Moses being one element among many Tolkien borrows from different places in building his own character and story.