While looking further into the question I posted above, I came across an Izumi City historical leaflet that describes the training of Uehara Masayoshi (shodai "Satsuma Masayoshi") as follows:
“At first he studied swordsmithing in the Takada tradition (Ōita City). Next, he learned the Naminohira tradition (Kagoshima City) under either Yamato no Kami Yasuyuki or Yasuchika. Furthermore, in the first year of Kyōhō (1716), he 'entered the gate' of the famous Sōshū tradition swordsmith of Satsuma, Maruta Masafusa. He made all three traditions entirely his own.”
「はじめ高田伝(大分市)について刀鍛冶を習い、ついで波平伝(鹿児島市)を大和守安行または安周から学び、さらに享保元年(1716)には、薩摩の相州伝名刀匠丸田正房の門に入り、三伝ことごとく自分のものとした。」
This passage describes a three-stage apprenticeship beginning in the Takada-den of Bungo (Mino-influenced Kyūshū style), progressing to the Naminohira-den (Yamato-derived Satsuma style), and culminating with Satsuma Sōshū training under Maruta Masafusa (so, here's the synthesis of Mino, Yamato, and Sōshū influences!).
The reference to early Takada-den training—which I haven’t seen anywhere else—suggests that the Bungo Takada school provided the shodai Masayoshi’s technical foundation prior to the Naminohira and Sōshū training that directly shaped his line’s late-Edo Satsuma work.
On the Naminohira side, the sequence Maruta Izu no Kami Masafusa, 2nd gen ->Yamato no Kami Yasuyuki -> Yasukuni -> Yasuchika is standard; given Yasuchika’s period of activity (1704–1741), he looks to be the likelier Naminohira teacher for the shodai (the leaflet’s “Yasuyuki or Yasuchika” probably reflects chronology confusion).
As for “entering the gate” of Maruta Masafusa, that can only refer to the 3rd-gen Maruta Sōzaemon Masafusa (1681–1716), not the Izu no Kami Masafusa (presumably 2nd-gen, 1658–1681) suggested in Sesko’s genealogy.
I suspect common claim that ”Masayoshi” trained with Masachika applies to the nidai or perhaps sandai generations. The pathway appears to be from Maruta Sōzaemon Masafusa (1681–1716) -> Mondo no Shō Masakiyo (1664–1730) -> Masachika (dated blades 1735, 1743). I wonder if there’s any primary documentation supporting this link, which represents a second Masayoshi line connection to Maruta Sōzaemon Masafusa via Mondo no Shō Masakiyo and his son…
This does seem to reconcile the confusing data I presented in my original post. I feel like I’ve either figured something out or fabricated a complete fiction. Problem is, I can’t tell which…
Any insights, thoughts, or comments are welcome...