(not so) Silly terminological question.

[regina pustet]

The instrumental vs. locative issue is a vexing problem indeed. In my
recent Lakota text collection, I sort of bypassed the problem, at least at
first sight, by glossing any locative prefix as L- (for locative, because
the meaning of prefixes in this slot is mostly a locative one), and any
"classical" instrumental prefix by INS-. The reader is then referred to
the grammar sketch which is part of the book, in which the different types
of L-prefixes and INS-prefixes are listed, and where their specific
functions are discussed. I think positing two groups of grammatical
elements for the L- and INS- positions, without singling out i- as a
special instrumental marker, makes sense especially from a morphosyntactic
point of view, since the L- and INS-slots are clearly separate
grammatically: L- and INS-markers can be combined within a given verb
form.

Another thing: what should we do with the derivational prefix i- which
designates instruments, i.e. nouns, as in i-cha'phe 'dagger' ("??-stab")?
This prefix is of course related to the basic locative/instrumental marker i-,
 but I think it is semantically distinct enough to be treated as a separate
marker, and therefore needs a separate gloss.

Regina