Those sources are tainted. There is an epidemic of fake listings on websites where once you call to inquire, it turns to a bait and switch where they say the fake apartment is no longer available and tell you "what else" they have instead.
The best solution is to contact the building but this is time intensive and you get a lot of spammy followup which is why we created https://fless.io to automate this process and help you find what is actually available and not just what zillow or the management company's website lists. It's still the best way to know what is truly available.