I’m digging up this topic only because it’s very interesting. Universal’s style guide is slightly more complex on cues. The long-story-short is that for them cues are essentially a glimpse into the full score, regardless of what part that cue is presented in. A few examples—
Clarinet 1 in B♭ cue in Horn 1 in F part: Cue is in B♭, labeled Clarinet 1 in B♭
Clarinet 1 in B♭ cue in Horn 1 in F part: Cue is in C, labeled simply Clarinet 1
Here’s the kicker — they have one exception!
Horn 2 in F cue in Horn 1 in F part: Cue is in F, labeled Horn 2 in F
If that doesn’t make your head spin, I don’t know what will! Think of the poor Horn player, juggling their C basso, B♭ basso, A♭ alto, G, and E♭ transpositions, then immediately prior to their entrance in that dreaded D♭ transposition they have a Clarinet cue transposed in B♭! Game over.
I will say there’s more precedent to this practice than Universal alone though, as a good deal of Wagner’s operas published originally by Schott employ this system, but for all my studying of parts, I have to say this cue system is in the extreme minority and I can think of no worse system.