If I understand you correctly, you are talking about a one-staff document with 141 systems - right?

And you need the numbers to appear to the left of each system - right?

You can still use the measure numbers, and adjust the measure number positioning so that the number displays to the left of the measure.

If a system has only one measure, then there is only one measure number in that system.

If a system has multiple measures, then only the first measure in that system should be included in the measure numbering

(look in the Measure Attributes: Measure Tool, double-click the measure).

Thanks, Peter, but that's not quite what I wanted. There are nearly 1400 measures in the piece, owing to the way I constructed it (most measures are 2 or 3 beats to allow easier moving of individual words to upper or lower staves); many of these are barless. Too many large numbers that would be distracting to singers! In a pinch I could use numbered rehearsal marks, but they would have to be applied individually to each staff and then manually moved to the left of each staff. Not very permanent, but doable at the very last minute. I'm still thinking about whether to do it or not. I'm revising a document that has been used for 20 years with no reference numbers except page numbers, so we've been getting along fine without them. Maybe an unnecessary enhancement.

Without knowing the actual Finale document it can be difficult to suggest the best solution.

Advice is only as good as knowledge of the project.

From your description it sounds like Auto-Sequencing Rehearsal Numbers will be the fastest solution.

I would duplicate the expression category Rehearsal Marks, and in the duplicate category edit the default positioning so that the rehearsal marks automatically will position themselves, where you need them (= no need to, manually move each rehearsal mark to the left of each system).

Then, in this new, custom category, create an Auto-Sequencing Rehearsal Number.

You will still have to add a rehearsal mark to each and every system, but that should not take long if you program an expression metatool.

To do so, switch to the Expression Tool, hold down Shift and a key (letter or number, e. g. the letter N key) on the computer keyboard.

Finale will display the Expression Selection where you can select your new expression with Auto-Sequencing Rehearsal Number.

To use the metatool, hold down the trigger you key you programmed (e. g. the letter N key), and click on the first measure in a system.