The earliest known reference to the Sonnets is in the Palladis Tamia [above] of Francis Meres, who speaks of them as “his sugared Sonnets among his private friends.” This was in 1598, and the next year two of them (138 and 144) were printed in The Passionate Pilgrim. We do not know that any of the others were published before 1609. - William J. Rolfe. Shakespeare’s Sonnets, 1883.

However, in 1594 only four years prior to Meres’ mention, there is an edition entitled Willobie His Avisa, with a most valuable critical introduction to Shakespeare and his Lucrece. To the date of the Sonnets’ composition, George Wyndham in his Poems of Shakespeare, published in 1898, tells of “a clue, so far as I am aware, unnoted, which may assist in dating the Sonnets, occurs in Sonnet 98. 1–4:

From you have I been absent in the spring
When proud pide Aprill (drest in all his trim)
Hath put a spirit of youth in euery thing:
That heauie Satume laught and leapt with him.

Our Poet, describing an absence in the spring, here associates Saturn with the burst of new life in April. A visual apprehension of Nature, at once accurate and sensuous, is a marked feature of his style, and, specially, in the case of the luminaries and of all effects of light in the heavens. The sun, the moon, “that full star that ushers in the even,” “the grey cheeks of the East” before dawn, “the twilight, after sunset fadeth in the West,” are noted with a vivid appreciation in Venus, Lucrece, and the Sonnets. And, again, in accordance with the prevailing belief of his age, he attributes occult power to the stars. “Indeed, he derives the ascription of “heaviness” to Saturn in this passage from books on Astrology: a science which seems to have engaged his interest no less than the other sciences of his day. Knowing the astrological characteristics of Saturn, he finds it effective to contrast that “leaden” planet with the exhilarating outburst of April. But he would not, I am convinced, have done so had not Saturn been a visible feature in the sky during the month of April to which he refers. To have dragged Saturn, without reason or rhyme, into a description of a particular month of April would have been a freak without a parallel in his poems.” - Wyndham: Poems of Shakespeare, 1898..