The astronomical observations recorded in the Diaries provide strong support for conventional chronology, but their scope is limited. Of the 180 Diaries preserved and dated, only six tablets record observations prior to 400 BC - four from the 5th century and one each from the 6th and 7th.
The 6th century tablet, Diary No.-567, records more than 40 observations that were shown in Feat of Clay to corroborate the date -567.
A similar study can be carried out on the oldest Diary, No.-651. A transliteration of the cuneiform text along with an English translation is provided for hardy souls who wish to evaluate the evidence.
These Diaries likely were composed shortly after the events they record. They are not reproductions. Generally, a scribe making a copy of a Diary registers the fact; he may write that a section of the original tablet is missing or otherwise refer to the document being reproduced.
The valid dating of the two oldest tablets shows that historians did a satisfactory job of reconstituting the Babylonian calendar used in the Diaries, at least back to -651. Still, the reconstituted calendar is not definitive. Several calendars were used in Babylonia, and tablets that contradict the conventional order of months have been found.
These unorthodox tablets do not subvert the established chronology. As long as the reconstituted calendar is fairly accurate, errors will not be cumulative. It may occasionally diverge from the true Diary calendar by a day or two, or even a month, but the calendars will realign after the period of disharmony.