Finding specific slides in various slide files - Keynote

I have literally thousands of slides amongst hundreds of various slide files. When I start creating a new slide file, sometimes I need a specific slide that I used in another slide file a few months ago.

I'm stuck searching through all my past slide files for that one slide I need.

Is there a way to tag or label each slide so I can do a search for a key word and all the slides pertaining to that keyword will pop up?

I have been using the search function in finder but even that has limitations and is not very reliable.

Perhaps there is a 3rd party software that is out that can help with this?

Any help is greatly appreciated.