Thank you again Dale !
Maybe I found an explanation : Naofusa's successor, Naotomo (Toryuken, Tachibana) seems to be confuzed with an Umetada namesake in old texts.
Looking for this explanation, I found too that some authors believe Toryuken was Naofusa, and some others believe he was an Hamano Norishige too.
Looking for answers make you find new questions, that's why it's fun !
Have a nice day !
JPB