I'm currently working on (among other things) a small, early 14C chronicle collection from the priory of Fineshade, which Cotton bound with a few other contemporary historical works to form Cotton Cleopatra D IX. The Fineshade manuscript contains transcripts of a few letters associated with Thomas of Lancaster's 1322 rebellion against Edward II, and a short chronicle of a few thousand words, written a year or two later (so before the deposition in 1327), narrating Edward II's reign in retrospect, as a story culminating in the events of 1322. The chronicler is not always correct in his facts, especially for the early years - he's far more accurate as he approaches the rebellion. However, where he errs, he errs in favour of improving the story.
For example, this author has the date of the Earl of Gloucester's death wrong. Gloucester died in 1295 (from memory), but here he dies after Edward II's accession, in the midst of the shower of ill-advised gifts that Edward is busy bestowing on Piers Gaveston, just so that Edward can also gift him Gloucester's daughter (Edward's niece) in marriage. This fits into the carefully structured 'gift crescendo' - royal money and treasure, then money and treasure extorted by taxes, then a wife of royal blood, then the earldom of Cornwall, all capped with a proverb about what sudden accession of power and riches does to a man's head. Gloucester’s death immediately preceding the betrothal, and perhaps acting as a catalyst for it, also fits with the theme of flouting the wishes of the dead patriarch. Just as Edward seems destined to ‘throw away’ all that his father gained, no sooner is Gloucester’s daughter Margaret left alone by the death of her father than the man who ought to have replaced him as her protector – her uncle the king - ‘wastes’ her on an upstart Gascon. There is probably also an implied parallel here between Margaret and the treasures “safely stowed [in the Tower] by his ancestors, so long ago that memory has faded”, which were also (according to this writer) given carelessly away to Gaveston.
The story, in this writer's hands, becomes a cohesive piece of literature in which the flaws that concern him most in Edward II's character are evident from his early years and provide the cause of all that comes after. They are even prophesied by Edward I before his death. The figures of Gaveston and Despenser stand less as players in their own right than as reflections (or strategic deflections?) of these crucial flaws in the king's character, embodying the financial mismanagement - first by inappropriate generosity and increasingly by violence - that in the view of this writer characterised Edward's reign.
There is also a more specific and interesting example of the evolution of a story in this manuscript which I think the writer did not intend. I should mention at this point that fragments of the collection, the chronicle among them, were published in the 1930s by George Haskins in Speculum and the EHR, but that, in examining the microfilm, I'm finding myself correcting Haskins far more often than I would have expected for a few pages of chronicle. There are, of course, some matters of opinion - but one of them, I really wish he'd commented on. Here's an image:
Full sentence, with abbreviations expanded into italics: "Quod rex ut audiuit grauiter mouebatur in animo & peticionem imporor[sic]-/tunam ferens indignanter ips?m ad terram deiecit pedibus que conculcauit dicens / totam regionem anglicanam per ipsum fore amittendam" - "And hearing that, the king was greatly moved in his soul and, taking the importunate petition, flung ? indignantly to the earth and trampled it with his feet, saying that he [his son] would give away the whole of the realm of England.This is early in the story, and it is what looks like a popular (and probably oft-repeated) myth of Edward II's early years. A better-known version of it is in the continuation of Walter of Guisborough's chronicle. We know that Prince Edward went to his father and asked him to grant the county of Ponthieu to Piers, that Edward I was rather displeased and refused, and that very soon after this, probably as a result, Piers was banished from England. Of course, we don't know Edward I's actual reaction - Walter of Guisborough's chronicle gives an extravagant account of Edward I's violent fury - he calls his son "fili meretricis male generate" (base-born son of a whore) and tears out as much of his hair as he can manage before throwing him out (ed. Harry Rothwell, Camden Society 89, 1957, pp. 382-83).
And here is another version of what seems to have been a popular story circulating: this chronicler has Edward I "indignantly taking the importunate petition [the physical object, presumably]" and throwing... something to the ground and stamped on it. And what that something is - the petition, or his son - depends on how you expand ipm.
Haskins writes ipsum without comment - masculine, so Edward I is physically attacking his son, as in the Guisborough version. And yes, when reading a chronicle or a series of letters dealing with politics you become accustomed to expanding abbreviated ipm as masculine, because it usually refers to a person and almost all the actors in these events are male. But there's actually no reason it can't be feminine ipsam, so far as I can see – and thus refer to the petition. The sentence would scan rather better syntactically, not to mention logically. Why take the chronicle just so that you can kick your own son? If the writer had wanted to avoid ambiguity he could have used a little 'a' above ipm (as below over abbreviated "tractati"), but this writer is not careful about ambiguities, and tends to go with muscle habit when it comes to abbreviations - see the quote above, where he absent-mindedly writes 'importunam' in full, but also adds a horizontal stroke to the stem of the p, which is the abbreviation for 'per' or 'por' (he does something similar a few page later, writing 'opprobrium' but adding a hook behind the first 'p' so that it technically reads 'oproprobrium'). And he is more accustomed to the single horizontal stroke about ipm - he's written it many times on the last few pages. To amend it, he'd have to stop and think about possible misinterpretations. Context is usually enough - but in this case, context fails him.
And that makes it interesting. Because a story with violence displaced onto a non-human object suddenly has the potential to have the violence directed to its cause, which rather disrupts the author's otherwise stable themes of proper and proportion use of power. Because any reader who loves drama who comes to read this manuscript later, without the author around to correct them, will be more likely to read ipsum than ipsam, because it's more usual. And - well, it makes a far more interesting and dramatic story, doesn't it? Particularly if they've also read the Guisborough version, and thus have the suggestion of violence in their mind. Fling the paper, or beat the son? Experience tells us which is likely to have the greater staying power.
 All quotes in this post are from f. 87r of the manuscript. I’ll post the text of the whole – and eventually a translation – when it’s tidied up.
 “A Chronicle of the Civil Wars of Edward II”, Speculum (1939): 73-81; “The Doncaster Petition, 1321”, English Historical Review 53 (1938): 478-485; “Judicial Proceedings against a Traitor after Boroughbridge, 1322”, Speculum 4 (1937): 509-511; for the latter see also George Sayle's correction of Haskins' error in “The Formal Judgement on the Traitors of 1322,” Speculum (1941): 57-63.
 He frequently leaves out or inserts 'et', or (in the Anglo-Norman documents) one or the other of commonly paired words like 'lige' and 'seygnur' in 'notre seygnur lige le roy'. Twice he skips an entire line, and several times he mis-expands an abbreviation. I think he must have had little time with the ms and been mostly working from his own notes in preparing the edition, because some of the errors just look like haste. Will post more about this at some point.
 This chronicler actually says Cornwall, rather than Ponthieu, which is the earldom Edward II gave Piers when he became king himself "iuxta sui desiderium prius conceptum & ordinatum" ("as he had already desired and fixed upon") - another example of retrospective narration, in which the story becomes smoother and more coherent.
 Given Walter of Guisborough seems to have died c. 1304, and this was supposed to have taken place in early 1307, this particular story can't have been narrated by him, but his successor seems to have inherited his flare for dramatic exaggeration and putting speeches into the mouths of his characters.