Let me quote from Markus Sesko’s book on Masamune:
“When it comes to dated works by Kunimitsu we are talking about a time from the first year of Einin (永仁, 1293) to the fourth year of Genkō (元享, 1324).
The Kotō Mei Zukushi Taizen (古刀銘尽大全) quotes Kunimitsu´s year of birth as Kenchō two (建長, 1250) and his year of death as Shōwa one (正和, 1312), which does not match with his known dated
signatures.
Well, the information from the Kotō Mei Zukushi Taizen, especially the dates, must be taken with a grain of salt because it gives for each and every smith his year of birth and death. Such a comprehensive
data was not known in earlier times and it is odd that the creator of this work suddenly “knew” all this at the time the publication was published for the first time, in the fourth year of Kansei (寛政, 1792).”
I think it eloquently describes why the veracity of that source is dubious.
And when it comes to Stan’s database, I do not think he has updated it recently. I believe that knowledge and understanding have moved substantially in the last 10-15 years since the database was put together. That is completely normal, as new blades emerge (well at least new / unknown to us) and the NBTHK keeps documenting new examples.