It is believed that there may have been an additional three paintings that formed the overall predella, one of which now resides in Zurich, whilst two other possible works have since been lost. Much of what we believe about all of these smaller frescoes as well as the overall altarpiece is derived from conjecture, rather than documentation from the period itself, though there is still a reasonably confident view on how these artworks would have originally been displayed because of what else we have learnt from Fra Angelico's career. The six episodes features here can now be found in the Museo di San Marco in Florence and each one is only around 23cm in width, which is entirely typical of the small nature of individual predella paintings. The artist would naturally keep a consistent size across each one so that they could be arranged in a tidy manner once complete.
These small paintings have been moved several times, once sitting alongside a larger piece by famous biographer, Giorgio Vasari, who himself was also a gifted artist. They have also been misattributed to some of Fra Angelico's other projects at various points, including his San Marco Altarpiece, though it has always been generally accepted that they were certainly of this artist's hand. Over time it has also been the common view that the pieces formed part of the Annalena altarpiece and there now seems to be no real controversy or disagreement over that view. Art from the Early Renaissance is frought with issues around attribution and a lack of documentation and so this situation is nothing new but over time at least these items can be discussed with a level of certainty.
There has been much discussion too around whether the main panel of the altarpiece arrived before or after the artist's San Marco Altarpiece, with many supporting the two different views. Most put the main panel at around 1434-1437, with these predella items then coming along in around 1437-1440. There is an obvious consistency in terms of style across these small frescoes which supports the idea that a single hand, Fra Angelico's, was involved in them all. There is also an issue with regards the condition of the main panel today which has made it harder for historians to drew solid conclusions about how the different elements of the altarpiece was produced, by whom, and when. Some have also suggested that actually the artworks for the predella were produced by a single assistant, from Fra Angelico's own designs and that this might explain why the level of quality is not to the same standard as the artist's work on the San Marco Altarpiece which arrived at around the same time.
The Six Episodes from the Lives of Saints Cosmas and Damian