I think you want keywords to do the job. If you want all photos with keyword Peter, this is a simple search. If you store a keyword for an event, then this is also a simple search.
So in your case, if you want to find all photos of Peter on Peter's birthday, you search for all photos that have both keywords. To do this, you use the Filter Bar, set the dropdown menu to keyword, select Peter, set the 2nd dropdown to Birthday, and that's it. A similar search can be done using smart collections.
Use the standard IPTC field "Job".
You’ve raised two somewhat separable issues:
- Going forward, what is a good method for managing “events”, to allow them to be searchable in combination with other keyword tags?
- How do you transition the folder-naming conventions of your existing 2000 folders to the new method?
Paige has recommended creating a parent keyword Events and creating a child keyword for each event. Then you use LR’s standard filtering and smart collections to look for photos in a particular event containing other keywords.
John Beardsworth has recommended using the IPTC metadata field Job (also called Job Identifier). With this approach also, you could use LR’s standard filtering and smart collections search.
Both approaches offer similar search capabilities. You can filter for both keywords and Job in the Library Filter bar, and you can search for both keywords and jobs in smart collections. However, smart collections let you test for exact match of the Job field, whereas Adobe inexplicably omitted exact match for keywords. This only matters if you have spaces in your event names, and even then, if you use “contains words” as the search operator, you’ll get reasonably close to exact match. (For example, Keywords Contains Words “Jermiah Birthday” would match the event keywords “Jeremiah Birthday”, “Birthday Party Jeremiah”, etc. but not “Peter Birthday”.)
An advantage of using keywords is that, compared to Job, LR has somewhat better features for entering an existing event and avoiding typos. You can use auto-complete in the Keywording Field, you can select the photo and then check the box next to its keyword in the Keyword List, you can drag a photo to the keyword in the Keyword List, or vice versa.
The Job field does auto-suggestion as you type, which is almost but not quite the same as keyword auto-complete. Auto-suggestion only works for event names you’ve already manually typed in, and it wouldn’t work if you use a tool to transfer your existing folder names to the Job field. There’s no way to use the mouse to drag an existing event to a photo or vice versa.
With keywords, you can see a complete list of all your existing events in the Keyword List field. But with the Job field, you could only see a complete list of the events in the Job column of the Filter bar.
With keywords, you can introduce a hierarchy of events, which may be useful for very large numbers of events. For example, you might have the subcategories Events > Birthdays, Events > Weddings, Events > Trips, etc. While you could use a naming convention for this in the Job field, the Keyword List panel makes it easier to view and navigate the hierarchy.
How To Transition From Your Folders
But if you use keywords, I’m not aware of such an easy method to transfer folder names to keywords. If you’re technically oriented, you could use the free Exiftool to append a photo’s containing folder name to its keyword field. If you’re not a tech geek, though, the learning curve on Exiftool is pretty steep. If you don’t use the IPTC Location fields in your photos, I think you could use Search Replace Transfer to copy the folder name into the IPTC Sublocation field and then use the plugin to copy that field to the keywords.
Going forward, if you will continue to maintain large numbers of events, I agree with Paige – use keywords, since LR has better facilities for maintaining and using large lists as keywords. It could be significantly harder, though, to transition from your folder names to keywords than to the Job field, but since it’s a one-time task, it is likely worth the effort in the long run.