(photos to left: Thirlby's annotations in Pope's 1725 ed. Beinecke Library, Yale University)
As it became more prestigious to edit Shakespeare and "correct" his play texts to accord with contemporary usage and theory, the cottage industry of conjecture commentary sprung up. It seems to have begun in earnest with Styan Thirlby (c 1691-1753), an acquaintance of Warburton and Theobald with whom he exchanged letters about Shakespearean emendation. Dr Johnson cited him freely in his 1765 edition.
Thirlby's annotations in 18th century editions exist in photostat and in ms. but are not in an easily accessible form, such as a printed book or a website. Some of his correspondence, fortunately, was preserved by John Nichols in letters exchanged with William Warburton and Lewis Theobald.
The conjecturing tradition continued into the nineteenth century and intensified as the preference for pictorial illustration over the variorum mode of detailed commentary became the norm with the Shakspeare texts produced. Commentary was an adjunct to the plays, but separate.
Correspondence between Warburton, Thirlby, and Theobald on editing