I understand this with a physical receipt, but if CC is anything like Microcenter you can't do a PM without voiding the original receipt. I was trying to do something similar with a PM on an Abit X2, SLI motherboard that was bought the last day the rebate was good. The next day the price was 20% lower. The manger told me I could get the PM next day no problem, but they would have to buy back the board and issue another receipt at the lower price. The manager told me the rebate company, whoever they are, has access to these PM, return-type transactions. They would see the original transaction was void and my new transaction now missed the rebate time-frame. Doesn't matter that I sent in the original receipt. They will see it as returned.
If CC rebates are done with this kind of rebate-house receipt access, the deal would only be good if you PM'd within the rebate time-frame. These guys are playing hardball with the deal-seekers.