Backwards compatibility v6, v7, v8

We have a set of users who have an old project using files created in v6.

Their assertion is that opening these files in v7 - we’re slowly migrating to v8 - “doesn’t work”. I am seeking clarification of what that actually means but, meanwhile, does anyone have a matrix of compatibility for the different versions? Should v7 be able to open, manipulate, edit and then save to v6 format?

yes, newer versions can always open older format files and write back to older version formats of Rhino.

There is also a very nice Rhino file conversion program posted in this topic. You can use it to convert Rhino 8 files as Rhino 6 files, for example. Make sure to download the latest version.