It seems to me there are 2 (good) ways a company can deal with this.
1. Don't give any release dates until it actually ships. Simply state it will be done when it is done. This works fairly well. Unfortunetly for FFG they officially stated that the game would be released at gencon.
2. If you can't do number 1 the best bet is to give constant and honest updates on the game. As an example every monday there would be an update on where the book is. If it is stuck at the printers just say so, etc.
I have seen both done and in general it kept everyone happy.