Notification when someone replied to a subscribed thread

OK, lately I keep noticing that I am not notified for some threads, though I did not see a pattern.

The latest thread that I was supposed to receive a notification is: VB - 128, 160 and 256 Bit File Encryption/Decryption with MD5, SHA1 and SHA256

I did not get ANY e-mail, and also, it does not show up in the subscribed threads (usually it comes on top).
And also... when I go in my "User CP" (main view) I can see a list of threads where I'm subscribed and there are new posts.

Nevermind, I just noticed I don't have a checkmark on the thread...
Since i'm sure that I did not un-subscribed to the thread, I guess the reson is because the thread is very old ? That's why it does not show up as subscribed ?

Can I mark ALL my old threads as subscribed ?