master copy
master copy {n.}
1. A perfect text to which all copies are made to conform; a corrected version used as a standard by printers.
The master copy must be right, because if it isn't, the mistakes in it will be repeated all through the edition.
2. A stencil from which other copies are made.
Mr. Brown told his secretary to save the master copy so that they could run off more copies whenever they needed them.
The master copy was too light so many of the copies didn't come out clear.
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Source: A Dictionary of American Idioms