I've been working with FileMaker for 30 years and just realized...
If a privilege group is prohibited from deleting a RECORD under certain circumstances, such as a boolean test of a flag field, the command is still available, not dynamically 'greyed out' for non-deletable records. It does, of course, conform to the privilege restrictions. You still have to rely on a script to re-test for delete privileges if I want to explain to the user that the command is prohibited, or at least avoid the "Error 200" message dialog.
Am I completely imagining that this used to behave differently or I forgot how to make the command unavailable on a record-by-record basis?
This has nothing to do with custom menus, as I suggested in the earlier version of this post.