I agree with Dan, I would expect the more you type the fewer candidates you see.
I don't know who Dan works for but he seems to be in the same situation that we are. We really only need to search addresses across a few counties. 90% of the time we are only looking in one county and don't even use city, state, and zip values. We do have some situations where we need to find addresses across a utility district that may cover portions of several counties but I still don't see that as a problem. The existing tool handles addresses across the entire world, so addresses with subunits across 8 counties shouldn't be a big deal.
No, I don't expect to scroll through 1000s of subunit addresses. I think this is a bad idea from both a performance and UI standpoint. We do have some locations with lots of subunits but most of the time it is a fairly short list.
I had not considered the "100 Main St, My City, My State, Zip (150 units)" idea but it is a thought. And if I could click it and see the 150 units that would be handy. However, if you have to click it to simply see 2, 3, or 10 units it becomes more cumbersome than useful.
I know this video doesn't come from an address locator but it does show some examples of subunits in our data set. Well, the video upload service isn't working right now so I will just include a link to the video: https://www.kgis.org/portal/portals/0/videos/misc/addresssubunits.mp4
Thanks for looking into this and I feel sure you guys will come up with something that works.
Bryan