Right-click your event or meeting tag
Click "Configure tag"

Content template
Default content, optional fields, show checkbox, base type

Replace "My new field" with "Date (Master)"

Scroll down and click "Make discoverable"

Right-click "task" supertag (or any other tag you want to add the master date tag to)
Click "Configure tag"

Right-click "task" supertag (or any other tag you want to add the master date tag to)

Default content, optional fields, show checkbox, base type

Click inside the Default content box & type '&gt;date'

Now you have the master date field in both your supertags!