Bridge search not finding all items

I am using Bridge in CS6.

I apply metadata, including keywords and descriptions to all images.

I use 'find' to locate ones without the data, for example "keyword does not exist"

Recently though, I realize, by remembering shooting certain subjects, that huge numbers are not turning up.

This is resulting in huge amounts of extra work, looking at each image's metadata to see if it is there.

For example, I shoot a lot of birds and give keywords such as sandpipers, or warblers.  Then when I go to add specific names in descriptions, it limits the number and I can group select and name a lot all at once when appropriate.  When everything has correct keywords and names, I move edited files to species specific folders arranged phylogenetically.

So now I find that I may have named some individuals, but the search missed dozens of others and I have to look at every one and do the process all over again.

I can't find any correlation with why some are found and others not, as keywords and descriptions.

Frequently I get a message 'can't read Bridge cache' but compacting, purging, resetting has not solved why hundreds may be invisible to such searches.  There is plenty of space and memory on the cache drive.