Multiple Layouts or Just One

[dotson]

... we do civil plan sets which can be up to 70 sheets.

Note that at one time (possibly still) AutoCAD is limited to 256 layouts per drawing.

[ScottHodges]

I have only been using sheet set manager since AutoCAD 2018, but never had problems with multiple sheets/layouts in one drawing. The title information is in the sheet set manager and the sheets call these using fields in text. My problem is using the same drawing file (such as standard details or drawings common to multiple discipline sets) in multiple sheet sets, which I would have thought would be a major use of sheet set manager, but is almost impossible to do without screwing up the sheet sets

[tedg]

I have only been using sheet set manager since AutoCAD 2018, but never had problems with multiple sheets/layouts in one drawing. The title information is in the sheet set manager and the sheets call these using fields in text. My problem is using the same drawing file (such as standard details or drawings common to multiple discipline sets) in multiple sheet sets, which I would have thought would be a major use of sheet set manager, but is almost impossible to do without screwing up the sheet sets

Congrats on your first post.
I think I understand what you're saying.
I would suggest setting up those common re-usable drawings as xrefs in MS in a standard place on your server, and simply create separate drawings in your project folder with the SSM info added.
You can pull layouts into your SSM from separate drawing files as well as the same file.
So in your case you may have a bunch of layouts for the main project in one file, and other layouts from a few common files such as standard details, notes or whatever, the SSM doesn't care.

Just a suggestion.