While effigies are an excellent resource for researching medieval armor, they must be used with some caution. Effigies represent the equipment of the elite that could afford them, not the great mass of ordinary men-at-arms.
Also, as Steve Muhlberger points out in response to an earlier post, "just because you have a pic of someone in a classy armor doesn't mean that person owned it." While some brasses seem individual enough to represent actual portraits, others are so stereotyped that they may owe more to the craftsman's pattern book than to the deceased's actual equipment and appearance.
While many brasses were ordered shortly after the death of the individual memorialized, this wasn't always so. Richard Beauchamp, Earl of Warwick's plans for his own memorial included a fine new chapel to put it in, and as a result his splendid bronze effigy wasn't cast until two decades after his death. In the other direction, Thomas, Lord Berkeley ordered a brass for himself and his wife upon her death in 1392. He himself survived for another 25 years.
His brass indicates the strain of flattering idealization visible in many effigies. His armored waist is scarcely wider than his helmeted head. It seems unlikely that he had such a slim profile in life. It would be interesting to compare the dimensions of the Black Prince's surviving coat armor with those implied by his effigy.
Effigies can also contain a number of symbolic elements that might never have been worn together at one time. Like many effigies of the late 14th and early 15th c., the head of the Black Prince's effigy rests upon a crested helm. By that period such helms were rarely worn outside the jousting or tournament field. At the same time, he wears a bascinet with a tall pointed skull of the shape often seen on the battlefield, but that couldn't have fit inside the helm. English effigies of this period continue to show conservative sleeveless coat armors even though illuminations from the same period show other designs becoming popular on the battlefield and elsewhere, including the short sleeved coat armor preserved above the Black Prince's tomb. The sleeveless coat armor may have dominated memorial portrayals because it was both traditional and well adapted to displaying arms on a two dimensional brass.
Prince Edward's effigy shows a sword by his side that is the acutely pointed shape of a contemporary fighting weapon. A tournament sword would have had a different shape, and a jouster would not have worn a sword at all.
Effigies were intended to show the symbols of the status, function and ancestry of the deceased gentleman: crest, sword and heraldry. If doing so required combining elements that wouldn't normally be worn together on any given day, so be it.