The Failed chronology adjustment of Silvester II.

Gerbert of Aurillac (†1003 ce.):

The most important scholar of his time and teacher of the young Otto III had accompanied the emperor to Rome and had been appointed by the emperor as Archbishop of Ravenna. As Pope Silvester II, after the sudden death of his predecessor, the 28-year-old Gregory V, he led the Roman Church into a new millennium of the Alexander era, after which Christianity and Jews counted the years [al Biruni].

Already in 1241Alx|930ce Aaron Ben Ascher had published the Masoretic Tanach, which had been worked out under consideration of astronomy.
The adaptation of the Christian traditions to the common standard of astronomers was therefore overdue:

Silvester ii

As the chronicle of Edessa reported, Christ was born in the 307th year of the Seleucid era. Surprisingly, it turned out that the traditions apparently lacked a 'Great Year' [Hipparchos] of 304 years. Furthermore, the lunar cycles of Callippos and Hipparchos had apparently been exchanged. Since the Indiction (Roman tax year) counted from 1 to 15 without interruption since Augustus until the present, another 7 years were missing in the tradition: Apparently an evil ruler (Phocas) had fallen under the of Damnatio Memoriae. All this could easily be corrected with a few 'additions' to the surviving texts.

When the Pope celebrated Holy Mass on Ascension Day 1003ce in the church of Santa Croce di Gerusalemme, near the former palace of the emperor's mother Helena, he collapsed. At last he gave order to dismember his 'cursed body' after his death and then bury it anonymously. Thus the rumour persisted that he had sold his soul to the devil before. But what could have that much shaken this pope? The Roman emperor's mother Helena was in fact the Greek-born daughter (†18.10.33 AD) of Marcus Vipsanius Agrippa.
She was the owner of the palace and S. Croce was her chapel. However, she was the mother of Caligula and not of Constantine the Great.

NB: Agrippina the Elder died on 18.10.33 AD, Helena died on 18.8.330 CE. If the 61 missing leap days of the calendar before -44 AD (253 ce) are considered, then both would have died on the same day!

The Pope's mass had put the Christian mother of Constantine on a par with the pagan empress who had lived three centuries earlier! Too late, Gerbert had realized that there was no longer any prospect of finding verifiable proof of the Savior's existence and thus for the truth of his teaching.

From his predecessor Gregory V, Pope Silvester II had taken over the imperial commission to 'purge the centuries'. With some pressure on the dioceses he had finally achieved this. The turn of the millennium, celebrated by the Pope as a secular year, provided contemporaries with the obvious reference for counting the years. Until then, the year of Jesus' birth had only been a time marker in antiquity, whose year was determined by the Greek's count, various worldly figures or the Roman cycles of indications.

In England there had apparently been some resistance to the specifications from Rome and the "unexpected outbreak of indignation and a state of affairs threatening danger" (Vita Bonifatii):

On 15 October 705 the Anglo-Saxon political institution of the Witenagemots (Council of Wise Men) met in Brentford near London to discuss the "propagandistic commitment to Rome-oriented church habits" promoted by Bishop Aldhelm.
    (Theologische Realenzyklopädie, volume VII, p. 69).

With the Continuatio Bedae the historiography ends there in 766 AD for three centuries up to the Norman conquest in 1066 CE.

"Eadmer v. Canterbury († 1124) omits [in his Historia Novorum in Anglia] a total of 223 years after Beda, which he thought were not worth mentioning and during this interval history therefore limps without the support of written history".   William of Malmsbury

[Another 118 years (616-734 AD) were taken over from Bede, which doubles 44 years (913-957 CE) - overall 297 years are missing].

Hock, C.F., (1837): Gerbert oder Papst Silvester II und sein Jahrhundert, Wien
Laszlo Renate (2006): Rätselhafte Zeitsprünge in England, Zeitensprünge 3/2006 S. 689.
Lausser, A. (1866): Gerbert – Étude historique sur le dixième siècle, Aurillac, Neuaufl.1966
Leo v. Vercelli (998) an Gregor V.: "Auf Befehl des Kaisers erschafft der Papst Jahrhunderte"
hek 1/2015