Also with Alamy, it's probably wise to go back and edit your caption putting some of it into the unsearchable description after the event is no longer newsworthy, though that is debatable.
For example, if you photograph a crowd waiting to hear X politician speak or Y band play at a festival, that would go into the caption, even is X or Y weren't in the image.
But because the caption is searchable, your photo would turn up on searches for X or Y.
Of course, it might be that in the future for some reason someone might be looking for a photo of the crowd at X's rally or Y's concert.
They must do something similar on Getty. Yesterday I did a Getty search on 'horse' and a lot of the top images didn't have a horse in them. Further investigation showed it was celebs at Cheltenham Festival, which is about horse racing, so presumably in the caption. I don't submit editorial to Getty, or anything else directly to them, so I don't know if you can change submission details afterwards. It makes for a messy search.