Jacques D.

Common feature called Machi shita-de yakiotoshi 区下-で 焼き落とし (i'm not totally sure of the Japanese writing)

The swordsmith is a big name rated jojo saku. I never talk about price,

I would add the wakizashi he talks about is gimei according Tsuruta san himself https://www.aoijapan.com/wakizashi-tanba-kami-yoshimichi-the-signature-not-reliable/

From Nagayama's book page 33

A tanto made the same year here : http://sanmei.com/contents/media/A69560.html

Just to add, the last pictures kindly shared by Sebastien are all of the Kyo branch

Yes mei reads Osaka ju Gassan Sadakatsu saku, but unfortunately it's gimei.

Yes.

I don't think so. I think that mei is an amateur invention. https://iidakoendo.com/7027/

I've never seen a book without errors unless it was peer-reviewed. As example Iimura (shinto taikan) attributes a sword to nidai Tadatsuna while it was made by the shodai, but i never seen a published sword which turns to be gimei.

It seems there's no Osaka yondai, i can't find it even in the Nihonto meikan (if i read it correctly)

Buy the sword not the papers, but if you pay a gimei the same price than a shoshin sword, i don't think you make a bargain.

Author of the shinto taikan is Iimura Yoshiaki

Imura's Shinto taikan

Fully agreed