Errors in publishing are quite common amongst all publishers.
Generally, it is not feasible to re-print the books to correct the errors.
Instead, they use the monies earned by sales of the books with errors in them
to then re-publish the books. They insert a correction sheet referred to as
an "Errata Sheet"

Errata Sheets Currently Available:

Master Keying Textbook Third Edition:
http://www.lounginglizardpublishing.com/MKTB_Errata.pdf

Master Keying By the Numbers:
http://www.lounginglizardpublishing.com/errataBBE.pdf

The Core of the Matter:
http://www.lounginglizardpublishing.com/TCMerrata.pdf

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