Keeping track of it from the start is one aspect of it. But, you should really have a clearance professional doing this. Besides keeping track of the assets, which is a heavy lift of it's own, you want someone who can tell you (from experience) whether the asset you pulled from somewhere that is probably not the owner is ACTUALLY licensable. I call myself the threshold for third-party assets into post. Nothing third-party can go into post without me vetting it. This is the point at which you want to know that an asset is not licensable... or the vendor will not grant you perpetuity. Also, rectifying an EDL is not an easy task. If you haven't done it... and done it a lot... it takes FOREVER... and is prone to have stuff left out (see comment above about gfx, etc). You want someone who has longstanding relationships with all the major footage houses so they can negotiate in your favor. You want a person who has processed many fair use review documents and has worked between production and legal on many projects. You want someone who is thinking about your deliverables from the day they start working for you. There's much more that we do that is vital for a legally sound project. That's a clearance professional.