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By the time of Jesus, the craft of document copying was certainly very advanced. The Jewish scribes had a long history and tradition of careful copying of their religious scrolls, and the Romans used documents extensively for administration of the Empire. There were both organized religious groups and private-sector operations providing copying services. Scribes were trained and employed in courts, temples, and libraries, and in places like Alexandria, where papyrus was manufactured, apparently copying services were organized businesses.
Because scribes were paid, manuscripts weren't simply copied. The amount of papyrus (or parchment) was calculated, the number of lines written were counted, and the content was proof-read and corrected during manufacture. Potential master-copies of existing works were examined for accuracy, and new copies were checked against the master-copy, and sometimes cross-checked with other good copies. A reasonably effective system for correcting mistakes had evolved in major copying centers, complete with special symbols and conventions for dealing with variations between copies.
Because of this, many mistakes were caught before a manuscript went out the door of the copying-center. Most people have heard of the "telephone game" in school, where children whisper a message in a long chain, and the end result is naturally a garbled message. But the situation with manuscript copying is quite different. Due to correction and cross-checking, the integrity of the copy is far better protected. This can also be represented by a diagram:
Because of copy-correction and cross-checking, manuscripts are actually embedded in a protective network or web, which helps to stabilize the text of each copy. The strength of these extra connections (and purity of text) is based on the quality of the proof-reading.
These extra connections and relationships between manuscripts created by cross-checking and proof-reading are not usually shown on genealogical trees (or stemmas), because the diagrams would become too complicated.
Because reliable master-copies can be used over and over again to produce new copies, manuscripts of widely varying dates can be equally good, and equally close to the original in terms of copy-generations. Realistic genealogical "trees" look like wide bushes rather than tall oaks.
The stemma below (from Edmer's 'Vita Wilfridi') is 'realistic' only in that it shows surviving manuscripts, not in that it represents a true picture of the actual copying stream with all the manuscripts:
Since errors only happen during copying or correction, and manuscripts can last an awfully long time without change, the actual date of manufacture or age of a manuscript is semi-independent of the "generation number" of a manuscript. What matters is not age at all, but rather three things control the quality of a text:
(1) the quality of the copying during each step,
(2) the quality of the correction during each step.
(3) The number of generations away from the original it is, because errors can be, but aren't necessarily, cumulative.
Nazaroo illustrated the independence of these two axis with his simple diagram and suggestion for a useful layout below:
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This idea was used successfully in the creation of a stemma for Lake's work:
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