In his epic chanson on the life of Bertrand du Guesclin, the Picard trouvere Cuvelier relates in great detail the French reconquest of Poitou from the English in 1372–73. In this the Constable took a leading part, culminating in his victory at the battle of Chize in late March 1373. Strangely, Cuvelier then omits all mention of events in the next few years. His long poem (completed by c. 1385) of almost 25,000 lines continues with a short account of the campaign that Louis, duke of Anjou, and Bertrand fought in Guyenne in 1377. Cuvelier then brings his work to a surprisingly abrupt conclusion with an equally partial account of the expedition that led up to the Constable's death at the siege of Chateauneuf de Randon in July 1380. Modern historians are aware that other significant campaigns in which Du Guesclin had an important role are also absent from the chanson; for example, those in Normandy and Brittany in 1378–79.

Cuvelier's modern editor speculates, surely correctly, that his motivation in bringing his poem to an end in this fashion was to avoid possible political embarrassment; otherwise he would have to explain his hero's ambivalent actions in 1379 when Bertrand failed to prevent the return of the exiled pro-English duke, John IV, to his duchy of Brittany. One very evident consequence is that numerous generations of later biographers, who have recounted the Constable's life simply by paraphrasing Cuvelier, with little effort to discover additional material, have often produced similarly distorted and very inadequate narratives of the Constable's last years. Georges Minois, for example, writing of the years 1375 and 1376, states categorically: ‘Deux annees de paix pendant lesquelles nous perdons la trace du connetable. Du Guesclin disparait des chroniques et des documents officiels.’

Even for those showing more initiative, other pitfalls await in arriving at a balanced or accurate version of events in which the Constable took part after 1373. The reconquest of Poitou was followed by the Breton campaign in the summer of that year; in it the Constable seized most towns and castles which had previously been in the allegiance of John IV.