That is exactly the predicament I was referring to that could cause an embarrassing and potentially difficult situation for a Canadian at the border. If the Americans have, in their records, information that they acquired a number of years ago, and subsequently that particular individual received a pardon, there could well be a conflict, on the face of the record, between what the American records show from historical data compared with what the facts are at the current moment. It would be useful to the Canadian to be able to say, “I can verify what my status is”, which you could do with a record suspension and you could not do with an expungement.
In terms of the exact retention period, I will see if I can get a precise answer from the Americans to answer your question. I suspect they retain previous information for quite some time, but I'll see if I can get a reading from American officials on how long they keep it.