I think there is a grace peiod before they become available, I thought it was 12 months though. but it allows for mistakes and overlooked registrations being stolen and sold back. Blame the cyber squatters for this.
Did you ask the domain registry that said its not available ???? They probably have more info
Maybe someone else is in the process of registering it, maybe its up for auction ??
Its a good quaestion, even if I don't have a good answer
Anyone know why domain names may not be available even though a whois search indicates they expired some time in 2005?

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