What is the documentary evidence that the complete Canon was listed before 400AD?
Biblical canon - Wikipedia
"Thus, while there was a good measure of debate in the Early Church over the New Testament canon, the major writings were accepted by almost all Christians by the middle of the 3rd century.
[32]" -wiki referenced above
"
Fifty Bibles of Constantine
In 331,
Constantine I commissioned
Eusebius to deliver fifty Bibles for the
Church of Constantinople.
Athanasius[37] recorded
Alexandrian scribes around 340 preparing Bibles for
Constans. Little else is known, though there is plenty of speculation. For example, it is speculated that this may have provided motivation for canon lists, and that
Codex Vaticanus and
Codex Sinaiticus are examples of these Bibles. Those codices contain almost a full version of the
Septuagint; Vaticanus is only lacking 1–3
Maccabees and Sinaiticus is lacking 2–3 Maccabees,
1 Esdras,
Baruch and
Letter of Jeremiah.
[38] Together with the
Peshitta and
Codex Alexandrinus, these are the earliest extant Christian Bibles.
[39]
There is no evidence among the
canons of the First Council of Nicaea of any determination on the canon, however,
Jerome (347-420), in his
Prologue to Judith, makes the claim that the
Book of Judith was "found by the Nicene Council to have been counted among the number of the Sacred Scriptures".
[40]" -ibid
-(I find it interesting Eusebius - an Arian Christian - was commissioned for the first 50 Bibles for Constantine, while Athanasius - from the polar opposite of Arian Christianity - is referenced for the Bibles being made for Constantine's son Constans.) It is notable the reference to Nicea, since it is often erroneously attributed that the canon was established at Nicea.
"The first Council that accepted the present Catholic canon (the
Canon of Trent of 1546) may have been the
Synod of Hippo Regius, held in North Africa in 393. A brief summary of the acts was read at and accepted by the
Council of Carthage (397) and also the
Council of Carthage (419).
[47] These Councils took place under the authority of
St. Augustine (354–430), who regarded the canon as already closed.
[48] Their decrees also declared by fiat that
Epistle to the Hebrews was written by Paul, for a time ending all debate on the subject." -ibid
-This would appear to be where "before 400AD" comes from.
"In a letter (c. 405) to
Exsuperius of Toulouse, a Gallic bishop,
Pope Innocent I mentioned the sacred books that were already received in the canon.
[55] When bishops and Councils spoke on the matter of the Biblican canon, however, they were not defining something new, but instead "were ratifying what had already become the mind of the Church".
[56] Thus from the 4th century there existed unanimity in the
West concerning the New Testament canon as it is today,
[57] with the exception of the
Book of Revelation. In the 5th century the
East too, with a few exceptions, came to accept the Book of Revelation and thus came into harmony on the matter of the New Testament canon.
[58]
As the canon crystallised, non-canonical texts fell into relative disfavour and neglect.
[59]" -ibid
-That about sums it up nicely.
-So to answer your question directly, (w)hat is the documentary evidence that the complete Canon was listed before 400AD?, the answer follows:
"Synod of 397
The Council of Carthage, called the third by
Denzinger,
[5] met on 28 August 397. It reaffirmed the canons of
Hippo from 393, and issued its own. One of these gives a
canon of the
Bible. The primary source of information about the third Council of Carthage comes from the
Codex Canonum Ecclesiae Africanae, which presents a compilation of ordinances enacted by various church councils in Carthage during the fourth and fifth centuries. In one section of this code the following paragraph concerning the
canon of Scripture appears.
[6]
16 [Placuit] ut praeter Scripturas canonicas nihil in Ecclesia legatur sub nomine divinarum Scripturarum. Sunt autem canonicae Scripture: Genesis, Exodus, Leviticus, Numeri, Deuterenomium, Iesu Nave, Iudicum, Ruth, Regnorum libri quatour, Paralipomenon libri duo, Iob, Psalterium Davidicum, Salomonis libre quinque, Duodecim libri prophetarum, Esaias, Ieremias, Daniel, Ezechiel, Tobias, Iudith, Hester, Hesdrae libre duo, Machabaeorum libre duo.
17 Novi autem Testamenti, evangeliorum libri quatuor, Actus Apostolorum liber unus, Pauli Apostoli epistolae tredecim., eiusdem ad Hebraeos una, Petri duae, Iohannis tres, Iacobi una, Iudae una, Apocalipsis Ioannis.
18 Ita ut de confirmando isto canone trasmarina Ecclesia consultatur. Liceat etiam legi passiones Martyrum, *** anniversarii dies eorum celebrantur
20 Hoc etiam fratri et consacerdoti nostro Bonifacio, vel aliis earum partium episcopis, pro confirmando isto canone innotescas, quia ita a patribus ista accepimus in ecclesia legenda.
(English translation-)
16 It was also determined that besides the Canonical Scriptures nothing be read in the Church under the title of divine Scriptures. The Canonical Scriptures are these:
Genesis,
Exodus,
Leviticus,
Numbers,
Deuteronomy,
Joshua the son of Nun,
Judges,
Ruth, four books of
Kings, two books of
Paraleipomena,
Job, the
Psalter, five books of
Solomon, the books of the
twelve prophets,
Isaiah,
Jeremiah,
Ezechiel,
Daniel,
Tobit,
Judith,
Esther, two books of
Esdras, two
Books of the Maccabees.
17 Of the New Testament:
four books of the Gospels, one book of the
Acts of the Apostles, thirteen
Epistles of the Apostle Paul, one epistle of the same [writer] to the
Hebrews, two
Epistles of the Apostle Peter, three of
John, one of
James, one of
Jude, one book of the
Apocalypse of John.
18 So let the church over the sea be consulted to confirm this canon. Let it also be allowed that the Passions of Martyrs be read when their festivals are kept.
20 Let this be made known also to our brother and fellow-priest Boniface, or to other bishops of those parts, for the purpose of confirming that Canon. Because we have received from our fathers that those books must be read in the Church.
— Enchiridium Biblicum 8-10"
Councils of Carthage - Wikipedia
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Discussions of establishment of Christian Biblical Canon are not difficult to find, so I presume your question is asking opinions?
The Old Testament Canon had already been established before the time of Jesus, in Greek (the Septuagint), though Christianity does tend to order the books a bit differently and minor edits to the text.
The New Testament is a bit more difficult, though all of the books settled on were in circulation in the second century. As I recall Revelation was the final book universally recognized, there were some "authorities" that resisted inclusion of that book. Likewise there were a few "letters" that were in popular circulation that didn't make the final cut (like the Shepherd of Hermas).
The Intertestamental Apocrypha is where there is a significant amount of leeway. The Catholic Bible (Douay, etc) includes the Book of Baruch, which is not included in any Protestant Bible. And there is no need going into the removal of the "graven images" part of the Ten Commandments, that discussion is well covered elsewhere. The original 1611 edition of the King James (Protestant) Bible contains a number of Intertestamental Apocrypha Books that were later excised, though the reasons I've read pertain more to publication costs than any authoritative pronouncement, and unfortunately it means most Protestants are not even aware these books are part of the authorized King James Bible.
So a good deal depends on what you mean by "canon," in that while there are certain Books universally acknowledged among Christians, there has always been a wee bit of fluidity as to what extra-Biblical Books are acceptable as well.
I will leave to Thomas to flesh out the details among the early Church Fathers, as that is his scholarly domain.