Are edits in one layout affecting others?

I count myself as being beyond the beginner stage by now, but I’m still confused by some behaviours in Dorico. An example: for an opera I worked on, I provided a vocal score first. Thanks to vigilant proof-readers, I had to correct the vocal score several times, on each occasion creating an incrementally dated pdf file to email to the client. I then worked on the full score, with the same routine. So both final versions are now ‘baked in’ to pdf files.
However - today I happened to glance at the Dorico vocal score and saw that various items had moved. I first thought that I’d selected the wrong choice for local/global settings when preparing the full score, and/or that (because I was a beginner when I started the project) the vocal score isn’t a part layout but a full or custom one. But I still can’t understand why - to select one instance - the dynamic for a note in the piano part had migrated elsewhere on the page, given that the full score doesn’t include the piano.
As it happens, there’s no problem, but if someone spots another error in either of these scores, and I need to correct them, I couldn’t be sure that something hadn’t moved elsewhere in the score. (For safety’s sake, what I’d probably do would be to save as pdfs only the page(s) with the new corrections, and do page replacements in my PDF editor .)
What I suppose I’m asking is: how do experienced users ensure that their various layouts remain unaffected by work on others?

Was the offending dynamic linked to other dynamics at the same position on other staves?

On the vocal score it only occurs once in the bar in question, viz. in the LH piano staff. In the full score it appears in the Bassoon, B.Tbn., timpani, cello and DB staves (there being no piano in this layout), and the B.Tb, cello and bass ones are indeed linked; the other two are independent.

By default, if you copy and paste music from one staff to another, dynamics and slurs will be linked. This goes for the Edit > Paste Special > Reduce function, too.

I suspect you created your piano reduction by copying and copying from your Bassoon/B.Tbn/whatever staves and then pasting/reducing to your piano staves.

It doesn’t matter whether or not the piano actually appears in the score layout - the dynamics and slurs will be linked if that material was pasted/reduced.

For what it’s worth, when doing this sort of work I ensure that this global Preference is unticked:

If you’re ok with unlinking everything everywhere (or at least dynamics and slurs in the piano staves but also in the source staves from which the piano music was copied), now would be a good time to Select All in the piano staves and unlink.

If you need to maintain the linking between the instruments in the full score, you could:
a) Untick that preference (apply and close)
b) Select all the dynamics in the piano staves (either via filtering or using Select More).
c) cut
d) paste (carefully - you need to ensure the first dynamic’s at exactly the same rhythmic position at which it was cut; the others should follow)

This will break the link for the piano staves only.

Thanks very much as usual, Leo. I shall certainly take all your suggestions on board. As it happens, the dynamics in the full score would have been copied from the piano to the other instruments (the vocal score having been completed before I’d started on the full score) but that comes to the same thing, I guess.
Other shifted material included stage directions, which I must have moved (in Engrave mode) in the full score when preparing that, without checking that they wouldn’t also move in the vocal score. More vigilance required on my part!

Chances are some stage indications have been moved in Write mode by mistake, in which case they will move in every layout they appear. Or Global was selected in the preferences… But still, I’d rather think that it’s a write mode user mistake.