It's a little tricky to explain. You see as you might know, you can subscribe to a thread either by posting in it or by manually subscribing to it, afterwards there should be an e-mail sent to you whenever a new reply is sent.
But sometimes it might take awhile before this feature goes in full effect (when it actually starts sending out those e-mails), so it may take awhile and you might have to refer to the board yourself a few times before then. Almost all the time when you aren't on serebii (in other words you left recently like say a day or so), it'll send you the e-mail for the most recent reply posted since you had left. In most cases, it won't send you anymore reply notices untill you come back on the serebii site (no matter where in the site you are), and then it'll send you a reply of any other replies that came in afterwards.
...... Ok, I lost you, didn't I?