There is no ICANN governance for releasing expired domain names, so consequently every registrar makes up their own rules.
NSI will hold domains until they are good and ready to release them - which means they can keep them for many, many months.
Your best bet if you are hot on this domain is to contact the prior owner and see if they can pay the renewal and then transfer it to you. The one good thing about NSI in this regards is they will often let expired domains be renewed many months after they expire.
-t
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