In chronological order:
From: 'Civil pleas 'extra coronam': (nos 470-523)', The London eyre of 1276 (1976), pp. 98-118. URL: http://www.british-history.ac.uk/report ... ery=corset Date accessed: 19 August 2012.[m. 19] Civil pleas (extra coronam) continued
508. William de St. Denis 'armorer' of London complains of Walter Hervy that when William was at peace in his house in the parish of St. Pancras on Saturday after the close of Easter 51 Henry III [30 Apr. 1267] Walter, then bailiff of the City of London, went to his house and took a hauberk, a horsetrapper (coopertorium) of iron mail of Chaumbliz, a (? lance head) (fn. 47) of iron, an iron corset (corsetum), a steel hat (capellum acerenum) and a basnet (basinum) covered with white leather, worth 14 marks; he carried the goods off and kept them against the peace, whence he says that he has suffered loss and damage to the value of 100s. and brings suit.
From: 'Memorials: 1297', Memorials of London and London Life: In the 13th, 14th and 15th centuries (1868), pp. 33-36. URL: http://www.british-history.ac.uk/report ... ery=corset Date accessed: 19 August 2012.Watch and Ward at the City Gates.
25 Edward I. A.D. 1297. Letter-Book B. fol. xxxiii. old numeration. (Latin.)
It was ordered that every bedel shall make summons by day in his own Ward, upon view of two good men, for setting watch at the Gates;—and that those so summoned shall come to the Gates in the day-time, and in the morning, at day-light, shall depart therefrom. And such persons are to be properly armed with two pieces; namely, with haketon (fn. 11) and gambeson (fn. 12) , or else with haketon and corset (fn. 13) , or with haketon and plates.
From: 'Calendar: Roll F: 12 May 1303 - 13 January 1305', Calendar of early mayor's court rolls: 1298-1307 (1924), pp. 142-169. URL: http://www.british-history.ac.uk/report ... ery=corset Date accessed: 19 August 2012.Membr. 6 26 Feb. 1303-4
Wednesday after the Feast of St Mathias the Apostle[24 Feb.]
Judgment that Garsias be acquitted; and he was enjoined to stay within doors after curfew so long as he remained in the City, and forbidden to do any harm to anyone either by night or day, under penalty of imprisonment.
. . . . . was found armed with iron corset and cap and a sword in the Guildhall in the presence of the Mayor, Aldermen, and many citizens. He was adjudged to forfeit his arms and be committed to prison.
From: 'Calendar: Roll H: 12 December 1305 - 12 November 1306', Calendar of early mayor's court rolls: 1298-1307 (1924), pp. 228-252. URL: http://www.british-history.ac.uk/report ... ery=corset Date accessed: 19 August 2012.Membr. 6 9 June 1306
Court of J. le Blound, Thursday before the Feast of St the Apostle [11 June]
Thomas, Rector of the Church of St Mary Wollechirchehawe, Guy le Clerk, and Richard le Coffrer, executors of the will of Thomas le Fleming, were summoned to answer Ralphde Wottone in a plea that they return to him one "gambeson" (fn. 1) ,one "aketoun," one "corset" (fn. 2) and one "banere," pledged with them for a loan of 13 marks, for which the plaintiff had paid 2 marks and a gambeson, value £10. Guy appeared and said he could not answer without his co-executors. Order was given to distrain them against the next Court.
It seems clear the corset is a form of defensive arms, distinguishable from "plates" (coats of plate, pairs of plate), and is made of iron. Dan suggested it could be mail. I initially rejected this since documents from this period commonly use lorica, hauberk, or some variant of haubergeon for mail armors, but it is possible that corset could be used for something like a sleeveless mail vest. I have never seen such a thing depicted in late 13th or early 14th century sources. The use of some sort of solid plate breast also seems unlikly to me for this time. Could corset describe a short scale vest?
In Osprey's Warrior Series #25, Italian Militiaman 1260-1392, Nicolle cites on p.54 a Bolognese law of 1288 requiring city militia to be armed with "panceria or caschetto, corsetto and manica de ferro gauntlets, collare or gorgiera, gambiera and cervelliera of mail, ciroteca body armour of iron" and a shield. ("Panceria" is probably mail, while the "caschetto" or little casque is obviouly a type of helmet. Presumably the corset reinforces this. I'm not sure why he thinks the "cervelliera" are mail coifs instead of cervelliere helmets to wear with the gambeson. ."Ciroteca" are, in fact, gloves.)
The important part being that "corset" isn't an armor term strictly limited to England in the late 13th century.
Anyone else have other examples, noticed something I missed, or have an idea what a corset might look like if it's not a CoP?