Yuccs - OL downfield pass blocking

Or anyone -Did you watch the seahawks packers game?  Seahawks ran a read option pass a couple of times.  First time was for a td.  How far downfield are OL allowed to be?  I tried looking it up but the rule book is vague to me!  It mentioned a yard downfield, but had many stipulations involved.  Looked to me that the seahawks had a guy 2 to 3 yards downfield when the ball was thrown.  Just wondering your take on this, thanks!