Prefabs keeping old asset references

Unity Engine
1

I’m looking into optimizing how many assets get dragged in when I load a prefab. I noticed some very old asset references in the prefab I’m loading. The member fields that are still in the serialized prefab were removed months ago, but the links to those other assets still exist, which is loading in assets that are ultimately unused, wasting loading time and memory.

  1. How do I remove these old references?
  2. How do I get more visibility into these stale references so I can clean them up more regularly? (I was lucky to determine they were there, as the assets were obviously old)

Thanks

2

Looking into this further, seems related to the m_Modification information that was added to prefabs. Here is a description of how to hand-remove them:
http://answers.unity3d.com/questions/1001665/why-are-prefabs-now-storing-a-list-of-modification.html