I agree. However, based on this statement and many others I have read, why wouldn't one put the actual contract price / sales price on the grid itself. It was under contract as of the effective date, at that price, so why not use it instead of the list price.
I would use the actual sales price, write it up as a contract and then explain below that it settled after the effective date (and prior to signature date) and the price shown is the actual contract / sales price. You could also adjust out the concessions on the grid as well, just explain it all below the grid. You could even put most weight on it if you wish, but present it as it was as of the effective date.