If PDFs are exported as Layered PDFs, the print vendor can more easily make the Marks layer non-printing/”off”, though getting a print vendor to recognize that a file is layered can be tough (because it’s so uncommon.)

I might also clarify: larger, more savvy print vendors with prepress systems probably prefer no marks (but the PDF still contains all Trim Box, Bleed Box, etc.)

Smaller, less savvy printers who ‘just do it the way we’ve always done it’ might freak out if there were no visible crop marks to confirm the artwork is correctly constructed.

Max,
We’ve been experiencing something similar using the “change fonts csv.jsx” by @kasyan-servetsky.

In our case, its not every Type 1 font fighting back, but merely some. While these tend to be font families that we have accumulated several versions and technologies, and often they share an identical Postscript Name, neither of the scripts mentioned thus far rely on postscript naming, and both work similarly in how they utilize the find/replace functions of InDesign to run.

It seems that if we can manually select a font to to find, and then the font to change, the scripts should be successful at doing this much faster, more consistently, and even in locked content.

So the issue appears to be more of how InDesign does what it has to do as a result of the scripts, but not the scripts themselves.

Looking for additional ideas, too!

I recently ‘cleaned up’ a Canva image provided by a client for T-shirt design. I did this by using Illustrator’s Trace feature, and for this particular art it worked surprisingly well.
Insult to injury, however, is the printing company (TeeSprings.com, a popular provider for YouTubers and content providers) only accepts raster images for their production process. After multiple conversations with their support, they have no current way to accept vector files for production.Yet in their limited posts regarding production, it appears that THEY then vectorize the image for correct production.
Sigh.

Doodlebug1 and Randi:
Have you resolved the issues?
If yes, would you share your solution?
If no, can you share a link to one of your documents (using dropbox, box, creative cloud, etc?)
There is version history in each InDesign file that would indicate version history, needed plug-ins, etc. and I’d be willing to take a look at it.

My experience is that needed plug-ins rarely, if ever, cause a file to not open.
I’m in agreement with others here that the most likely cause is version related.
And knowing it’s a complex world, yep, there could be something else at play.

To the topic: a non-scripting solution:
If you have an images subfolder for each part (flute 1 pages 1-12, flute 2 pages 1-12 etc) and each page file with identical filenames you could simply relink your document to the graphics in the part you want to create. The graphics will initially show as modified, but you know that all are produced identically and the swap is safe.

Sidebar:
Why would your publisher continue to use a tool released in 2002?
With more recent versions of InDesign, you could have multiple layers (one for each part) and ultimately you export the book x number of times, with just one layer active. To create each part, you could duplicate and rename the previous layer, and drag-n-drop the new part eps onto the existing.
The efficiencies gained right there would seem to make buying a new PC and the software worthwhile in productivity, accuracy, etc. You are correct that scripting could improve this even more.
So what is stopping them? (asked seriously.)