They forgot about poor Haruna?

Not so sure for the long texts.

In short, he thinks the reference material he used had error.
He later found daily publication that mentioned another date which resulted in data where Haruna is not constantly docked for 8 years like in this comic.
So he's writing an apology letter here.

According to Japanese Wikipedia, Haruna's reconstruction was temporary halted due to the Naval Treaty of Washington that was held on 1921, which restrain countries for building larger capital ships. Haruna left active service and was assigned as a practice ship, her reconstruction resumed on 1924, then her first major reconstruction was on 1926, she was the first Japanese vessel to receive extensive modernization, it was completed on 1928, she was reclassified as a Battleship.

Kinda ironic since Haruna still hasn't receive her Kai-Ni upgrade.