Appending metadata (instead of overwriting it) with template?

Question

We have thousands of images we had a student intern tag with IPTC Core metadata.  Some of what he did is good, for instance, his titles and captions are spot on.  But some things, like Creator fields and copyright status are all over the place (my fault for not saying exactly what we wanted in those fields).  I've created a metadata template in Bridge with just those fields I want to update and standardize checked, and things like caption and title left unchecked (image of template).  I had hoped that when I applied it to his images, just those fields I had checked would have their information overwritten and those that were left unchecked would be left unaltered.  Instead what I'm finding is that the ones I've checked are being updated like I want, but the ones left unchecked are being changed to blank entries.  Not good, in fact, that's bad, as it represents a whole lot of work down the drain.  Fortunately I made a copy of the images the student updated and have been experimenting on the copies, so nothing is lost yet, but I'm no closer to solving the problem.  Is there a way to do this, or do I need to do them one at a time?  Thanks for any insight you can give!

Answer 1

The long and the short of it is Adobe is going to do away with my Caption (Description) created in IrfanView no matter what I do.  Doesn't even recognize it, even though they are there when I open the image(s) in IrfanView.  If I add the same information in via Bridge and then open it in IrfanView, it shows up exactly as it did if I had just created it in IrfanView.  My confusion stems from the fact that some of the images were tagged in Adobe and some in IrfanView, so there appeared to be no rhyme or reason as to what was going on and why some times it overwrote the settings and other times it did not.  To make matters worse, no all of IrfanView's tags get overwritten.  Creator, for instance, remains, unless I tell Bridge to Replace instead of Append.  If I say replace, it replaces that field with whatever I have in the template.  If I say append, it adds what's in the template alongside what was added in IrfanView.
The thing is, these are all being tagged to be added to a Gallery Server Pro system, which can extract the metadata and use it to make the galleries searchable, and Gallery Server Pro doesn't care which program added the data, it sees them both just fine.  So now I'm thinking about just using IrfanView and eschewing adobe altogether.  Unfortunately, Adobe is easier to use, but if I go that route all 1600 images will have to have their captions re-added in Adobe.
I need a drink.