I've noticed for a while that even movies with generally well-made costumes have a tendency to consider stomachers worn only with formal clothing.  John Adams, for example, shows Abigail ca. 1775 in a plain gown with an anachronistic center front closure for working around the farm, but in France (ca. 1785) in a fancy silk gown with a stomacher.  (One also sees this to an extent with re-enactors, helped along by older research that calls center-front closures accurate from 1770.)  The perception seems to exist because it's simpler to close a gown with both bodice edges together than to incorporate an extra piece.  As I am joining a re-enactment group and am preparing to make my own ensemble, I wanted to do as much research into not-completely-formal stomachers as possible to make and back up my own choices.

 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 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.