Valid content will not be detected when applied to a no-planned overprint.
When turning overprint on, other valid contents are also disabled hence cannot be inspected.
✅ Getting your overprint settings just right.
✅ Standardize in layers.
✅ Standardize on the name to a Comprehensive Name.
✅ Use dieline in a unique layer.
❌ Mix content with Die-line or information layers.
❌ Use the same value color of the dieline and varnish invalid contents.
The following steps describe how to view information about an Overprint in the PDF :
In Adobe Acrobat
Tools → Print Production.
Choose "output preview" after opening this tool.
Change your "preview" to " color warnings".
Then check the box "show overprinting".