John,
If you have Bridge (part of PS), do you use keywords? Of course you can keyword with other programs too. I've pretty much keyworded all my RR images, so in Bridge, for instance, I can search for all photos of a class of steam NP engine, taken in the 1940s, freight or passenger, and location. This will narrow it down to a few images, all displayed.
On new images, I'm pretty careful to do this and file info when I add photos to the hard drive. It only took me about 5 years to do this will all the scanned negs and slides! I mostly would scan 5-20 at a time and add this info as I went. Once done, it makes finding things a lot easier. I've done about 5000 RR images now, lots of work, but I feel it's worth it.
Steve