I print out a new copy of my big planning grid, fill in everything I want or need to keep, and then alternate glaring at it, and going for walks, until I can start filling in new bits where they belong:
http://emmadarwin.typepad.com/thisitchofwriting/2010/05/help-yourself.html
If I don't know some bits further on, I don't worry too much because as I work my way towards that part, cutting and shutting and moving and embroidering and expanding, I usually find that the answers sort themselves out. As far as I'm concerned, the grid isn't about representing the whole novel, it's about helping you to see the shape of it and how all the bits fit together.
FWIW, I know people who use a version of this with one column for each character, but it wouldn't work for me like that, because the whole point is that a column represents a strand of the plot.
The other thing I've done recently - but you may not have time for this - is to write something like a synopsis, although I prefer to think that I'm telling myself the story, in the new version.
There's something about having to turn it into consecutive sentences which express a chain of cause and effect, which really makes sure that your chains of cause and effect connect up. And of course you don't have to polish it at all, unlike a synopsis for sending-out purposes.
Good luck!
Emma
<Added>Having said that, once I've got the grid roughed out, I make myself a little plan of campaign. Quite often it just says "Work through from Ch 1, making all changes". But sometimes it's obvious that one piece of work depends on having done another, in which case I make myself a checklist.
And my default is working forwards, whatever the morning's job is - that way you're less likely to get wound up in a cocoon of missing chunks and floating scraps.
Oh, and I'm sure you've thought of this, but do it on a new copy of the file. Keep the old one, so if all else fails you can revert to factory settings.