We've has some really wet stretches around here, and I've never seen a daylily turn yellow like that from overwatering, although I think it can happen. In my opinion, daylilies like to dry out between waterings, so if you're having a wet spring, I wouldn't be doing any extra watering. They store a lot of water in their root systems and don't need to be wet constantly. And I think if they are wet for too long, they can get root rot. Which might be your problem.
My out of the box guess is, to me it looks like maybe they got hit by a weed killer. Just this spring I turned a daylily and some ground cover yellow by accidentally getting too close with the Scotts Weed and Feed I was using. If I was going by the last pic only, I'd be pretty cocky about that guess because the one closest to the lawn is doing the worst in that picture and it could have been hit with "weed and feed". But the first picture... someone would have had to go out of their way to put weed and feed on that one. So, maybe not a good guess, but I'll throw it out there anyway.