Hi there
I´m a Windows user, so I don´t know if this applies to you, but I had some problems with Bridge collections and had to try and rebuild them.
I´ve found that the metadata is embedded in the files themselves, but Windows support metadata straight from the filesystem, I don´t know on the MAC.
All I had to do was tell Bridge to make a new “smart collection”. It rebuilds the collection by searching the files while looking for the set of metatags that you want in that collection. Simple.
The metatags were associated when I´ve created the collections the first time, so if you associate metatags to your files, it stays with the files no matter where you move them.
I hope it works for you!