The kind of thing that happens in historiography

Quoting from wikipedian article Primary Chronicle

The historical period covered in the Tale of Bygone Years begins with biblical times, in the introductory portion of the text, and concludes with the year 1117 in the Chronicle's third edition. Russian philologist and founder of the science of textology, Aleksey Shakhmatov, was the first one to discover early on that the chronology of the Primary Chronicle opens with an error. The Chronicle has it that “In the year 6360 (852), the fifteenth of the indiction, at the accession of the Emperor Michael, the land of Rus’ was first named.”[5]: 58  However, 11th century Greek historian John Skylitzes' accounts of the Byzantine history show that Emperor Michael III did not begin his reign in 852 but rather a decade earlier, on January 20, 842.[6] Because of the work's several identified chronological issues and numerous logical incongruities that have been pointed out by historians over the years, the Chronicle's value as a reliable historical source has been placed under strict scrutiny by the contemporary experts in the field (see “§ Assessment and critique”).

So, at a key point, it is ten years off, unless it is Skylitzes who is ten years off.

It says other "chronological issues" and "numerous logical incongruities" and in the section mentioned we get things left out because they didn't fit and invented even if not there.

It can be mentioned that the Novgorod First Chronicle is considered as a corrective.

A N D it may be mentioned that the study leading to these assessments were started by one Aleksey Shakhmatov who was a Czarist and therefore a Great Russian nationalist at some level./HGL

PS - other example. We know the Church Historian and Hymnographer died in Mytilene one 4th of Huly - but was it 712 or 726 or 740? Wiki gives all three alternatives!/HGL