en.wikipedia.org/wiki/Yata_no_Kagami

This sentence conflicts with Kokugakuin University's Encyclopedia of Shinto, which records the fire of 9 September 1040 (Chōkyū 1) and states that the divine mirror (yata no kagami) was also damaged in that blaze. In other words, the mirror was not undamaged.

A second Kokugakuin Encyclopedia of Shinto entry also explains that the reproduction of the mirror kept within the palace is the one that repeatedly faced such disasters, noting that it "is said to have narrowly escaped destruction in disasters on several occasions." That description is inconsistent with a flat claim that the mirror simply "was not damaged" in the 1040 fire.

So, while the mirror may have survived the fire in some form, the article's stronger statement that it was not damaged is contradicted by the cited reference work.

This is a calendar-era error. Chōkyū began on November 10, 1040. That means an event in the 9th month of 1040 cannot be dated to Chōkyū 1; it still fell in the previous era.

Kokugakuin University's Encyclopedia of Shinto chronology places the palace fire on 9.9 and then separately notes that the era name was changed to Chōkyū only later, on 11.10, because of calamities including that fire. Kotobank likewise states that the Chōkyū era began on 1040-11-10. So the article's combination of "1040" + "Chōkyū 1" + "9th month" is internally inconsistent.

The event may well have occurred in 1040's ninth month, but if so the era should be Chōryaku 4, not Chōkyū 1.