When you are planning your change effort and finding the right people to be involved, look for institutional knowledge. You need to know where this resides because it can both benefit and hinder your efforts.Recognize the positives of having people involved with your change effort who have a lot of institutional knowledge -- they can:
Help you figure out how to get from here to there. Their knowledge of the organization as it is today will be invaluable in understanding your current world. It's from this basis that you'll be able to figure out who all of the impacted stakeholders are, what current communication channels exist and which ones reach the people you need to connect with most effectively.
Navigate the pathways of the organization. Their connections to and knowledge of the true power brokers (whether official or unofficial) can make or break you. You need to identify everybody who will need to be persuaded to be a champion and change agent for you -- and an organizational chart doesn't always give you the whole picture.
Point out hidden "gotcha's". They've been around for a while and they can tell you why prior efforts have failed. What were the factors that caused something to fail, and what were the reasons that something succeeded?
Tell you who you need to get on board. The people with institutional knowledge will know the people who are effective at getting a job done -- and they may be one of those people themselves. Find out who they recommend you enlist!
Also, recognize that somebody with institutional knowledge has the potential to derail your efforts. For all of the same reasons they can help you, they also have the knowledge to go around behind you and cause you to fail. So, make sure you know where they stand!