Thank you Kai for your first impressions
.
Thank you Philip for your essay. I should instantly assume my fault to make you think i have a pair of examples. In fact it is only one that i have, with pictures taken from both sides; which somehow reduces the consistence of this being a modified plug bayonet in the context. Notwithstanding i catch your idea only that, in this case, i would attend to there being more differences in its configuration than similarities to be one of those ... as i am now revisiting R.D.C. Evans THE PLUG BAYONET.
On the other hand i was not daring to reject the Chinese idea for myself and now i feel more inclined to accept such exclusion, although not dismissing that this would have been one of a single scabbard pair ... as opposed to the less plausible hypothesis of it being a secondary 'knife' going sheathed to a larger main sword scabbard.
Examples you quote in Army Bianche Italiane are superb, by the way.
Yes, the guard shape is intriguing, looking early ... European ?
And yes again; this blade, unless having been subject to skilled manipulation, which is highly improbable, looks definitely earlier than XIX century.
Muito obrigado.