I see the same situation, in my case only the Piccolo moved. Closing and re-opening the file did not apply the specified change to any other instruments.

Have you apprised Support of this via the "Submit a request" link above?

The menu items are somewhat misleading, should be singular, not plural:

Position Name > Full Staff name

Position Name > Abbreviated Staff name

According to the manual these commands only affect one selected staff name at a time:

“Choose these commands to set up the position and alignment for the selected full or abbreviated staff name.”

But …

Is there a reason why you are not using the command above to, instead set the default name positions?

(Staff menu > Set Default name Positions > …)

Peter, thanks for the quick response! I guess it's good to know that it was my expectations that were off, not the program behavior...

Valid question about "Set Default." That was indeed the first option I tried, and nothing happened. I thus assumed it was similar to setting fonts for staff names, where a "default" only helps you when you create new staves but a separate command is needed to change existing ones.

After you asked, I went back and experimented more. It appears changing the Default Staff Name Positioning DOES affect a number of hidden sketch staves at the bottom of my score, but nothing in the staves that are actually being displayed. Default Group Name Positioning has no impact on any of my groups.

So you appear to be right, in theory there is a way to adjust multiple names at once, but -- joy of joys -- it's simply not working.

Thanks!

… I went back and experimented more. It appears changing the Default Staff Name Positioning DOES affect a number of hidden sketch staves at the bottom of my score, but nothing in the staves that are actually being displayed …

From your description it sounds like some of the staff names have been repositioned manually, so that they are no longer at the default position.

… I thus assumed it was similar to setting fonts for staff names, where a "default" only helps you when you create new staves but a separate command is needed to change existing ones …

In my experience all staff names at their default position will be moved, whereas staff names that have been manually moved to another position than the default position, will not be affected.

This is by design, and what users have requested.

You can move a staff’s name back to the default position.

This is done in the Staff Attributes, just de-select the two check boxes for Staff Name Position:

Full Staff Name Position

Abbr. Staff Name Position

Ah, yes indeed that's exactly what's up. Still, removing the positioning and then re-positioning as a batch is on balance better than having to set each line individually, so thank you!