I’m afraid updating to Dorico 5 wouldn’t help in this case, as the option in Notation Options to use global bar numbers has been removed. It’s not ideal, but I think you might find that overriding the rehearsal mark index property to match the desired bar number might work.
Thank you for the reply, Daniel. I tried changing the rehearsal mark index property on one of the parts, and it still shows and empty box where the rehearsal mark should be. Then, I tried changing it globally on a rehearsal mark in the score. Score still displays correctly, but parts have blank rectangles.
Also — are you saying Dorico 5 has essentially given up on being able to have rehearsal marks as bar numbers when there are individual time signature changes in parts, even if they are equivalent?