I'm somehow just baffled why you're giving up. I mean, you've only looked in one place. If I did my surveys at work like that, Cheat Mountain Salamanders wouldn't exist in the area just because I didn't find them on one survey (which are 5-6 hours long, by the way, and done once or twice a week). My point is that you can't just count it out after looking in one spot. And you won't always find them, even if they are there. It's a matter of perseverance.
As for finding them, it depends. It depends on how many are there, how much food is there, weather conditions, etc. If you've never found adults in the area, chances are they're not breeding in that pond. If there ARE adults in the area, they may still not be breeding in that pond. That doesn't mean they aren't there. But then, even if you're in the historical range, that doesn't mean they ARE there, either. If you're in the range, but not in the right habitat, you're not going to find them. That would be like looking for pythons in the ocean. Yeah, you may be in Thailand, but most pythons don't usually dwell in the ocean.