Inconvenient ‘Shared Column’ in Document Set

Have the following design for a light-weight business process:

1. a Document Set to collapse all documentation involving a review process – the document to review, and accompanying documentation, review sheets, explanatory documentation, and so;
2. the Document Set preset with a document template for document to be reviewed;
3. a SharePoint Designer workflow associated with the content type of the document template to steer the review process;
4. and a workflow on the docset library to "archive" the docset once the review on contained document is completed.

The 2nd / outer workflow is required in addition to the inner workflow on the contained document, as a SharePoint Designer workflow does not give you access to the logical container Document Set.

Challenge is how to communicate from the inner to the outer workflow. I thought about doing this via a shared property between docset and contained document. However, here SharePoint exposes one of its peculiarities: although on level of the contained document it appears as if you can set the shared field (it is editable in editform for the contained document); in reality the edit is ignored. Whether done explicit manually in the editform, or automated set in the workflow on document. The 'Shared Column' is strictly owned on the containing DocSet level, and it's values plus changes in that pushed to all the contained items.

Note:This Sharegate post describes how-to hide the Shared Columns in the Edit Dialog as they are actually not editable on Document Set contained level; so that at least your end-users will not get confused.

As it turns out, the concept of 'Shared Columns' can still be used to trigger from the 'inner' workflow on "contained" document, a waiting condition in the 'outer' workflow on DocSet. The key is to use 'Update item in Current List' in the inner workflow, and set the 'Shared Column' direct on the DocSet by selecting it via a matching value between 'contained' document and the DocSet. Inspiration coming from post SharePoint 2010: How to update Parent Folders Timestamps when Child contents have been modified'.