Elisabeth Schüssler Fiorenza (Revelation, 160ff) and David Aune (Revelation 1–5, cxff) each list out attempts by scholars to reconstruct earlier sources incorporated into the Revelation. A number of them find a pre-AD 70 source and a later one, but the contents vary considerably from one scholar to the next.
Erbes saw three main Christian texts within the Revelation, from AD 40, 62, and 80, respectively. Charles thought parts of the book predated AD 70, and suggested the final editor was ‘stupid’, ‘ignorant’, and ‘celibate’. Ford believed Rev 4–11 came from John the Baptizer; 12–22 came from a later student of John’s theology, who was probably a follower of Jesus; Rev 1–3 and 22 were written by a Christian redactor.
Kraft said the Revelation was from one author, who revised it multiple times over the years, and was not concerned with conveying a linear chronology. Rousseau saw five layers of redaction: the core being five plagues (an early form of Rev 16), with two subsequent Judean redactors and then two Christian redactors. Sabatier believed the Revelation was originally a Christian text, and that Judean oracles were inserted throughout it, with some final additions afterward.
Vischer argued the Revelation was originally a Judean apocalypse that was then Christianized. Völter saw the Revelation as beginning with a core ‘Apocalypse of John’ from about AD 65, which was redacted and rearranged four times over the following three decades. Weiss decided the Revelation combined two different apocalypses, a Christian’s from AD 66–70 and a Judean’s from AD 70, which were combined by a Christian around AD 95. Weizsäcker believed there was just one author, his book comprised of three series of seven (the seals, bowls, and trumpets); these were then interrupted when the author brought in other sources to expand his work. Weyland thought the Revelation was made of two Judean apocalypses that were combined and Christianized.
Especially noteworthy is Stierlin […] Aune was so unimpressed with Stierlin’s reconstruction, he called it ‘virtually worthless for scholarship’ because Stierlin ‘essentially atomized the text’.

Aune’s own reconstruction of the Revelation’s sources posited three layers across several decades, but all from one author updating his own text. The primary stage contained twelve ‘apocalyptic tracts’, a series of related, but distinct units. These are still in their original order, spread across Rev 7–22, and were written through the AD 50s and 60s, some of them possibly written before the author became a follower of Jesus. The official ‘first edition’ of the book was written in the wake of Rome’s conquest of Jerusalem in AD 70; here the author took his twelve tracts and wrote some insertions to bridge them together; if the author had not previously been a follower of Jesus, this is when he Christianized his earlier work. The final ‘second edition’ came more than a decade after the first, with the first few and last chapters added, along with smaller changes made to stress Jesus’ unity with God.
Revelation is made of three layers: a Christian apocalypse structured around three sets of seven (seals, bowls, trumpets), a Jewish apocalypse with a more mythological theme (the dragon, the beasts, the prostitute), and a Christian redactor who edited them together within an epistolary framework (chapters 1-3, 10, most of 22, and smaller interpolations throughout).

Stierlin’s reconstruction:
Apocalypse of Two Witnesses 11.3–5a; 6–8a; 9–13

First Apocalypse 22.16; 1.3ab; 10.1ac, 2a, 3–4 8–11; 11.1–2; 13.11–14a, 14c–18; 17.8; 14.9–11; 11.19; 6.9–11; 15.5–6, 7b–8; 16.1, 10ab, 12, 3–7, 17b; 19.11, 13a, 14, 15b–16, 19; 20.9; 14.17–20; 6.12b–14; 15.2–4; 20.13a, 4, 13c; 21.3–4; 22.5; 16.10–11; 19.9c

Second Apocalypse 22.6c–7; 4.1–4, 6b–8a, 9–11; 5.13–14a; 14.1–3, 4b–5; 12.7–8, 9c–11; 15.1ab; 16.2, 10c–11, 8–9, 17a, 21; 17.3–7, 9a, 18, 9b–10, 12–14; 18.4–8; 16.18–20; 14.8; 18.20, 14, 22–23; 19.4–5; 7.1; 8.7–10, 11b–12; 20.1ac, 3bcd, 3e, 4c–5; 16.13–14, 16; 20.9c–10; 14.6–7; 14.14, 15c–16; 20.12; 21.1–2, 16ab, 12, 14, 21c–23; 19.9ab, 10; 21.6–8, 5c

Third Apocalypse 1.1b–3; 4.1–8ac; 12.1–3b, 4c–6, 9ab, 4ab, 15–17; 5.1–11, 14b; 6.1–8, 15–17; 12.18e; 13.1-8; 17.1–2, 18bc, 15, 12a, 16b–17; 18.21, 24, 1–3, 9–13, 15–19; 19.13; 81b–5; 7.2, 3b–8; 8.5, 13; 9.1–11a, 12–21; 11.14; 10.1, 2bc, 5c–7; 20.1–2a, 3, 4cfg, 6–8; 19.17–18, 21b, 20ad; 11.15–18; 20.11ab; 19.11d–12, 15a, 13b; 20.11cd, 13bc, 12, 15, 14; 21.4d, 5ab; 19.6–8b; 21.9ac, 10–11a, 15, 16c–21b, 13, 12def; 22.1–4; 21.24–27; 22.8b–9, 12–13, 17, 14–15, 6a

Letters 1.1ag, 2a, 4–8, 9–20; 2.1–3.22; 22.20–21

Stierlin shredded the Revelation in his efforts to ‘reconstruct’ his five proposed sources. Very little is left in its traditional order, and numerous fragments of sentences were attributed to different sources. Aune was so unimpressed with Stierlin’s reconstruction, he called it ‘virtually worthless for scholarship’ because Stierlin ‘essentially atomized the text’.
the incredibly complex way in which Stierlin proposes the final document was compiled is difficult to justify. When ancients compiled sources into new compositions, they simply did not work in the way that Stierlin’s reconstruction requires.
Revelation has three layers:
One source contained a highly structured, Hekhalot-like vision that sees the eschaton as a new exodus: it begins in the courtyard of the heavenly temple (Rev 4-5), passes the altars of burnt offering and incense during the seals (6-9), bowls (15-16), and trumpets (8-11), and concludes with the opening of the innermost room (11.15-19) for the final judgment (20.11-15).

Another source (comprising most of Rev 12-14; 17.1-20.10; and 21) that incorporated a variety of late Second Temple apocalyptic traditions (especially those shared by 4 Ezra and 2 Baruch) and influences from Greco-Roman cultural (e.g. Apollo vs Python; Roma the goddess seated on seven hills; Nero Redivivus), and conveyed them through an overtly mythological framework adapted from Dan 7-12.

A Christian redactor combined the above two, slightly rearranging parts, and situating them inside the epistolary framework.
Revelation Draft Hypothesis:
The Revelation Draft Hypothesis, sees the book of Revelation constructed by forming parallels with several texts in the Old Testament such as Ezekiel, Isaiah, Zechariah, Deuteronomy, Joshua, Exodus, and Daniel. For example, Ezekiel’s encounter with God is in reverse order as John’s encounter with God (Ezek 1:5–28; Rev 4:2–7) note both accounts have beings with faces of a lion, ox or calf, man, and eagle (Ezek 1:10; Rev 4:7), both accounts have an expanse before the throne (Ezek 1:22; Rev 4:6). The chariot’s horses in Zechariah’s are the same colors as the four horses in Revelation (Zech 6:1–8; Rev 6:1–8). The nesting of the seven marches around Jericho by Joshua is reenacted by Jesus nesting the seven trumpets within the seventh seal (Josh 6:8–10; Rev 6:1–17; 8:1–9:21; 11:15–19). The description of the beast in Revelation is taken directly out of Daniel (see Dan 7:2–8; Rev 13:1–7).