We use project documents, because of the issue with item documents incrementing as described in this post. However, when a document is linked to an item that document is not included in bulk export. For ECOs and programmatic BOM releases, it is very time consuming to individually download each document. There is also a large element of risk that the user will need to check every BOM item for a linked document. In a BOM that is over 3000 lines, this is unrealistic for us to brute force our way through.
