This question came up in 2009 when speaking to Shigekazu 'Jimmy' Hayashi about my sword, as the NBTHK papered it as a naginata-naoshi katana, not a nagamaki. Jimmy's reply was essentially as I've written here that for the NBTHK nagamaki fall under the heading of naginata, and without knowing the specific history the NBTHK is going to designate it as a naginata.
Following that discussion I began to dig further and found in a published article, which I now have to find again, that the mounts determine whether a piece is a nagamaki, and unless the history is known the NBTHK will use the designation of 'naginata' .
Notice that under the 2nd image the description reads;
"This sword was described as "Naginata naoshi katana" in the exhibition guide."
Notice that under the bottom image the description reads;
''Both the swords above were described as "Nagamaki naoshi katana" in the exhibition guide.''
Clearly one sword has a naginata hi and the other does not.
Edited by nagamaki - Franco, 12 March 2017 - 10:34 PM.