It could be that when they initially go on sale online the club doesn't physically have the tickets to post out. All my tickets have turned up in time although on a couple of occasions it has been the day before the match.
You might be able to phone up and arrange to pick them up from The Amex or failing that a pick up from Elland Road. If you are going to The Amex tomorrow to get tickets do it before 11am as they take the tickets off sale at that time for a Saturday away game.
Last season they didn't use B1 when we were there , on other visits we've been in the South East Corner ("cheese wedge") and also once when we've had 4 blocks of the South Stand plus the "cheese wedge".