How much time and effort should a writer put into consistency? And how much energy should an editor devote to it? The answer, as with many editorial issues, is not that simple, but it is easy to elucidate.
A book or a book-length publication, such as an extensive report, must for the sake of a reader’s respect for the authority of the argument and/or the regard of the care taken by the writer, strive for flawless consistency in all regards. But note that “flawless consistency” does not necessary mean “precisely the same every time.” If not, what does it mean?
When an entity, whether a person or a company or organization, is mentioned repeatedly in one document, of course the name should be spelled correctly each time. But there are acceptable variations to the treatment of the name. When a biography of Sir Arthur Conan Doyle, for example, names him for the first time, the reader should see those four components of his name.
But his last name alone is sufficient thereafter — with exceptions. An emphatic reference to his strength of character may require a stylistic flourish: “But Sir Arthur Conan Doyle wasn’t about to let her get away with that.” A quotation in the book may refer to him before he was knighted, or the person quoted may simply have omitted the honorific. Complicating matters, it appears that later in life, the creator of Sherlock Holmes preferred to use “Conan Doyle,” though without a hyphen, as his surname, so the writer must decide whether to use the single surname or the double version — and must do so consistently.
By the same token, a company or organization name is often spelled out only the first time it is used, and is then referred to by a short form (for example, Dow, rather than Dow Chemical Company) or an acronym or initialism (NASA, rather than the National Aeronautic and Space Administration, for instance). As with a personal name, there’s no reason to revert to the full name outside a quotation or some other anomalous usage.
And what if a book is a collection of essays by various writers? The editor of the anthology is responsible for establishing a style that remains consistent throughout — unless, of course, one or more contributions are previously published in a differing form of the language, such as an essay by a British English writer among American English authors. The editor may edit the essay to conform to American English style, but it’s easier to leave it as is and acknowledge the discrepancy in the introduction or in a note.
As for treatment of names, an anthology’s editor might choose to resume full forms at the beginning of each chapter to reacquaint the reader, then resort to short forms or abbreviations after each chapter’s first reference.
In the case of words with more than one correct spelling, such as adviser/advisor, the copy editor simply notes the preferred spelling on a style sheet while working on a manuscript and performs a word search for any instances of the nonpreferred spelling and corrects them. Alternatively, the copy editor can simply note that the manuscript, as edited, conforms to the primary spelling in the dictionary. (Many publications use this policy as a simplifying default setting to prevent ambiguity about which spelling to employ.)
Periodicals, as well as book publishers and many other companies and organizations that publish, generally have a style guide, which prescribes treatment of pertinent names and terminology; for example, an industry-focused magazine about architecture may routinely refer to the American Institute of Architects by its initials alone because the publication’s readers do not require a complete identification, and a journal about US history will dictate that all references to indigenous bovines specify bison, rather than the inaccurate popular variant buffalo.
A carefully compiled style guide will document these policies, and a diligent copy editor will consistently honor them. (Writers are often unaware of the rules governing editorial inconsistency, or are not careful about applying them, and in the worst cases do not think doing so is their responsibility, or even necessary.)
Web sites with user-generated content, as opposed to those that, like print publications, have an editorial staff, cannot expect all contributors to conform to style and will thus be flexible about consistency, though any text generated by the site staff should adhere to the prescribed style.