English isn't a compiled language. We can offer expressions that violate its "rules" and are still effective and powerful. It cannot be any other way. We know from Godel that no logical system can be consistent _and_ complete, so the use any human language must either admit violations of principle or accept limitations on what can be said in that language. It is the quality and success of the expression, not its compliance with grammatical rules, by which we judge expressions. The tests are "do you know what is meant" and "could it be said better", not "is it grammatical".
There are, therefore, no hard and fast authorities on English usage. English has principles and precedents, but not rules, and good writing is that which uses or violates those principles to communicate effectively. Shakespeare isn't an authority on usage, he's a compendium of examples of how usage can be harnessed for expression.
Now following those principles, and leveraging the readers' understanding and usage of them, allows far more expressive sentences. Gibbon writes enormous sentences that are clear as water and more efficient than any possible revision. Lincoln, by mastery of grammar, was able to express himself both powerfully and precisely. But the rules are in the service of expression, and good writers depart them when they don't permit the expression of what they want to say.
Complaints about the "mistakes" of great authors are generally mistakes about what the other meant to say, or insistence on some compliance that would damage brevity or power or nuance without adding any clarity. On ten minutes googling Devlin, I couldn't find a single "mistake" whose correction would clearly improve the sentence. Several of his examples miss the point, or weaken the sentence.
But if you want an authority, go to C.S. Lewis:
"About amn't I, aren't I and am I not, of course there are no right or wrong answers about language in the sense in which there are right and wrong answers in Arithmetic. . . . Don't take any notice of teachers and textbooks in such matters. Nor of logic. It is good to say "more than one passenger was hurt," although more than one equals at least two and therefore logically the verb ought to be plural were not singular was!"
http://www.lettersofnote.com/2012/04/c-s-lewis-on-writing.ht...