Thanks, this is what I suspected. Now I just have to figure out what makes only certain places in the score a special case in which a good sight reader might need a reminder verses the many other places in which no reminder is included.
Harmony mostly, or very similar patterns and chords...
And, of course, highly chromatic/atonal/weird works!
I just put courtesy naturals every next bar, in order to cancel the previous one and remind the performer of that, especially since I rarely use key signatures to begin with... Naturals are there ONLY as courtesy accidentals.
And I also use them in chords where both C# and C natural can be found (in the same chord), in which case I put the natural to avoid any kind of confusion.