In the previous chapter the chronology of a stage before the ‘Chronicle of Ireland’ of 911 was reconstructed using the papal and imperial items. However, this does not necessarily represent the original chronology, because these items must have been included after 725, when Bede's CM was written. This is much later than the period when contemporary recording can be identified in the Irish chronicles, so it is possible that kalends were already lost or added before the papal and imperial items were included. The following discussion is an attempt to go back further and reconstruct the original chronology of this chronicle where possible.

It has long been established that an important source for the Irish annals before ca 740 was an ‘Iona Chronicle’, containing most of our surviving items describing events in Britain as well as at least some of the Irish items. There is strong evidence to suggest that this chronicle was in existence by 660, but before then the situation is much less certain; the number of events recorded in the Irish annals is lower, and it is not so apparent that the items only derive from chronicles. Other chronological texts, such as Easter tables and king-lists with reign-lengths, could have provided items, as potentially could other sources with little or no dating, such as hagiographical texts, genealogies and tales.