Jonathan Swift, Gulliver's Travels, orig. pub. 1726
"A-La-Mode, 1754", The Gentleman's Magazine, 1754
Mr. Town, The Connoisseur (vol. 2), 1755
The Spectator (vol. 8), 1755
Abraham Tucker (as Edward Search), The Light of Nature Pursued (vol. 1), 1768
The Hibernian Magazine, 1781
The following prints are given as examples of closures as much as actual stomachers.
"High Life at Noon", 1769
"Lady's Maid Soaping Linen", 1769
"Lady Betty Bustle and her Maid Lucy Preparing for the Masquerade at the Pantheon", 1772
"A Pleasing Method of Rouzing the Doctor", 1775
"The Extravaganza", 1776
"Rural Masquerade", 1776
"The Cork Rump", 1776
"College Breakfast", 1783
Some of these, the prints of maidservants, show bodices lacing almost closed over the front - it's not actually clear whether they're laced over a stomacher or just the stays. What I find just as interesting is that so many prints have the front of the maid's dress hidden: yes, sometimes it's just because of the woman's position or what she's holding, but very often it's completely obscured by a very large kerchief.
This is probably not very interesting research and everyone else knows this already, but I have this urge to find everything out on my own, just to make sure.