All this just to continue the last post.
1) Horst Fuhrmann points out two things in connection to Pseudo-Isidore and the Recognitiones: First, it looks like at least a few Carolingian-era readers were skeptical that the Recognitiones was genuine. Second, according to all the most authoritative chronological sources (Eusebius, Jerome, Bede), James predeceased Peter by seven years (dying in A.D. 61, whereas Peter was thought to have clung on until 68). Insofar as it is possible to be in error about the chronology of vaguely legendary religious figures like the apostles, then, Pseudo-Clement is in error. Perhaps the second point explains the first. In any case, Pseudo-Isidore seems to be unaware of this fact: While our forgers inherit the outlines of the first two Clement letters, both of which are addressed to James purportedly after Peter's death, the fifth Clement letter in the decretals is also from Clement to James, also purportedly drafted after Peter's death, and is entirely of Pseudo-Isidore's making.
2) Here's a fun fact about Pseudo-Isidore: Clement aside, the forgers never invent more than three letters for any pope. Another fun fact: With two important and very marked exceptions (Damasus and Leo), if Pseudo-Isidore includes genuine letters from a given pope (as happens frequently in Part 3, where genuine decretals come from the HGA, and sometimes the Dionysio-Hadriana and the Quesnelliana as well), he does not include any forgeries in the name of that pope.
At first glance, Clement seems to violate the first of these principles -- Part 1 includes five Clementine epistles. But the Pseudo-Isidore only invents the last three out of whole cloth, so in fact you might call Clement the exception that proves the rule . What about the second of these principles, though? Doesn't Pseudo-Isidore invent three letters for Pope Clement, while also including what some at least thought to be genuine letters for the same pope? Here again, a closer look is illuminating. Though in Clement's name, the first two letters are primarily devoted to relating apocryphal precepts of Peter the Apostle. So in a way, you might say that the collection has two decretals for St. Peter and three for Clement. The first two for Peter are interpolated but based upon arguably "genuine" material (not really but anyway), and the three for Clement are forged. All this fits perfectly with the rhythm of the rest of the collection.
3) I mentioned it last time, but it's worth repeating: The seam between Recognitiones material and Pseudo-Isidorian material in the first Clementine letter is really obvious and clumsy. I also cited Seckel's theory: that starting out with the two Clement letters was an attempt to make the whole book look familiar. But if that was the purpose, why handle the transition so poorly? Why interpolate a known text so clumsily? Is Pseudo-Isidore in fact exploiting contemporary doubts about the authenticity of the Recognitiones here? Is the implication that this is the real letter from Clement, which got truncated and appended to the inauthentic fairy-tale of the Recognitiones? It's worth noting that the letters that Pseudo-Isidore forges in Clement's name are chock-full of Recognitiones passages, many of them favorable to Pseudo-Isidore's agenda. Clearly he found the text sympathetic.
Post corrected (bolded text above).