Could you provide more details about OS and system version and exact CS5 version numbers.
Are you using different disks (internal, external) or a network set up or do all the files reside on the same disk.
Sometimes read and write permissions change for what ever reason and this can also cause problems for Bridge.
But asside from that Bridge is not very good in acting as Digital Asset Management for archive purposes and collections can be very useful but to my opinion only for a short period and not when you need to rely on them for a long time. If you need to use this for a longer periode I woudl suggest to also add the name of the collection as a keyword. In that way you have a good escape to find choices back.
