This page illustrates a set of different breastplate shapes that existed during the 16th c. All of the examples were taken from the Allen collection.
The first three illustrate a form that was used in the late fifteenth century and into the second decade of the sixteenth. It is often associated with Flemish and Spanish usage, but a similar form occurs in Henry VIII's silvered and engraved armor. It is characterized by a central keel on an overall rounded form.
The first illustrates a late 15th c. neck line which rises high over the shoulders and much larger angular rolls. The second would be more typical
of the early 16th c. and the third in between with its high shoulders, but also high center of the neck.
The rolls on both of these breastplates are rolled "out." This is typical of 15th and very early 16th c. construction.
In the early sixteenth century breastplates changed in form along with the form of civilian costume. This illustrates the more full and rounded form typical of early 16th c. clothing. In this case the surface is plain.
By this time the roll construction has switched to the method used throughout the rest of the 16th c. The rolls are flaired out and then rolled back toward the inside.