Remove the 'lastUpdated' field from the Asset metadata summary. This is an internal field that tracks when the metadata record has changed, and users don't care about it.
Add two new Date fields to asset:
blobCreated - touched when a blob is first attached to the asset
blobUpdated - touched on creation, and when a new blob (i.e. different hash) is attached to the asset
Rename lastAccessed to lastDownloaded for clarity (e.g. it refers to when the content was downloaded, not when someone last had a look at the asset metadata through search/browse)
Add the two new fields to the Asset summary.