SteamDB is already going to have most manifests past 2013 that were ever in a non-passworded branch. You can see that list by going to a depot page and clicking the manifests tab. Workshop manifests will be ignored. Submitted manifests will be later checked on CDN and will be added to the database if they still exist.

Format: depotid_manifestid like 232251_173982683433347217

It is regexed, any garbage around it doesn't matter.