When I read Gary Rich's post on The Perseverance Test and Joseph I thought about "failed" prophecies.
 
When God gives me a word of prophecy which takes years to come to pass I encourage myself to persevere with a little known verse in the Psalms: "Until the time that his word (Joseph's) came to pass the Word of the LORD tested him." (Joseph had prophesied about his dreams 13 years earlier. Certainly looked like he missed it.)
 
Once you know for certain the dream, prophecy, word of knowledge etc. came from God, do not ever give up on it. Sometimes God is testing us. At other times He is getting us ready to receive. Sometimes it simply takes years to bring all things into alignment.
 
One note of caution as you wait in faith; Don't help God along with the prophecy. Sarah did that and birthed an Ishmael. Our part is to pray and trust. By the way, it's ok to ask God questions about the prophetic word. He will let you know if it is not time to explain to you further.
 
Be blessed,
Shelva