From Early Christian Writings
"Since it was discovered in a monastery in Constantinople and published by P. Bryennios in 1883, the Didache or Teaching of the Twelve Apostles has continued to be one of the most disputed of early Christian texts. It has been depicted by scholars as anything between the original of the Apostolic Decree (c. 50 AD) and a late archaising fiction of the early third century. It bears no date itself, nor does it make reference to any datable external event, yet the picture of the Church which it presents could only be described as primitive, reaching back to the very earliest stages of the Church’s order and practice in a way which largely agrees with the picture presented by the NT, while at the same time posing questions for many traditional interpretations of this first period of the Church’s life. Fragments of the Didache were found at Oxyrhyncus (P. Oxy 1782) from the fourth century and in coptic translation (P. Lond. Or. 9271) from 3/4th century. Traces of the use of this text, and the high regard it enjoyed, are widespread in the literature of the second and third centuries especially in Syria and Egypt. It was used by the compilator of the Didascalia (C 2/3rd) and the Liber Graduun (C 3/4th), as well as being absorbed in toto by the Apostolic Constitutions (C c. 3/4th, abbreviated as Ca) and partially by various Egyptian and Ethiopian Church Orders, after which it ceased to circulate independently. Athanasius describes it as ‘appointed by the Fathers to be read by those who newly join us, and who wish for instruction in the word of goodness’ [Festal Letter 39:7]. Hence a date for the Didache in its present form later than the second century must be considered unlikely, and a date before the end of the first century probable. "
The Didache, also called The Teaching (or Doctrine) of the Twelve Apostles, is a short treatise that dates back to the early Christian Church and was accounted by some of the Fathers as next to Holy Scripture. It was probably written in Syria during the second half of the 1st century, although some scholars suggest a 2nd-century composition.
The first part of the Didache is a moral treatise describing the Two Ways, the Way of Life and the Way of Death. The second and third parts contain instructions on baptism, the Eucharist, fasting, prayer, matters of church organization, apostles and teachers, prophets, bishops, and deacons. The Didache is perhaps the first text to append a doxology to the Lord’s Prayer: “…for thine is the power and the glory unto all ages.”
Although partially paraphrased in other ancient documents (see, for example, the Didascalia Apostolorum below), the Didache was practically lost until Philotheos Bryennios [1], Greek Orthodox metropolitan of Nicomedia, rediscovered/published it in 1873/1883.
Not to be confused with the Didascalia Apostolorum, Teaching of the Twelve Holy Apostles and Disciples of Our Saviour, a 3rd century text founded upon the Didache [2], [3], [4]. "
You may be correct it may not have been counted AS scripture…just NEXT to scripture.