Welcome to the wonderful land of expired domains.
If someone has the real story, lay it on us, but here is what I have picked up in my pursuits of expired domains:
1) All registrars hold the domain for a number of days (40 I think) after it expires. This gives a fair chance to the owner to register it. This happened to me and I was EXTREMELY greateful for the delay.
2) Now, here is where it gets funky. In my experience all registrars (EXCEPT NSI) release the domains after the 40th day. THis is without fail as I have seen lists of expired domains at Name Winner (http://www.namewinner.com
) and the day they are due they are available. I know they aren't NSI domains due to the fact that the WhoIs record the day before they drop shows a different registrar.
3) As for NSI domains ... I haven't had one drop yet, but I have only been buying expired domains for 4 months. I think there was some talk that they were hoarding the domains in an effort to create an auction for them. Also, Snap Names is owned by them. Snap Names allows you to bid on domains that are about to expire. Hmmm, no conflict there ;-)
Anyway, this is all based on my personal experience and what I have learned observing the process ... I may be totally wacked out on this, though.