I assume that you changed your setting, which will effect threads that you subscribe to moving forward, however it won't work retroactively. You'll have to handle these manually.

If you go to MyFlyerTalk, under the subscribed threads it says "View all Subscribed Threads". Click that and look at the "Notification" column. If it doesn't say "instant", then you need to change it. The very far right column is a check box. Check all that you want instant notifications for and scroll to the bottom of the list. There you will find a drop down with the option "Instant Email Notification". Select that and hit "GO". This should update those threads subscription settings.