If you need the most up to date, use the actual registrar of the individual domain (Enom, Dotster, Godaddy, etc). The second most up to date will be the registry operators as follows:
I had several experiences with situations like these...
I have seen domains which were available but the next day (doing a whois again) seemd to have been regged some years ago... Sound and seems very strange...
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I took it that the question was where to find the most up to date info on registered names.
But yes, I have heard of names being registered after someine checked the whois but didn't register immediately. I think it was more common name generation sites and reseller sites though. Most I've heard have been several years ago though, not recently.
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