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davidcyclebackMajor restoration, like building up of corners, is usually staightforeward to identify. It's a lot easier to identify than a ironed wrinkle.
If a card is horribly damaged, like torn in half, even the top conservator can't fix it to be undetectable. With the naked eye, you will be able to see where the tear was.
My neighbor was a professional painter and restorer, and I've checked out a number of his restored paintings. One he fixed after his grandson threw his shoe through it. The restoration is top notch, and the casual visitor won't notice anything, but you will see where it was restored if you look closely. Much of the restoration was major, ala repairing a hole where a kid threw a shoe through the middle ... He told me conservators have a tough time conserving Jackson Pollack paintings, because Pollack put cigarette butts and stuff in his paintings. It can be a challenge on how to conserve a cigarette butt.
Interestingly, he collects 1700s British silver pitchers, much which has been restored. I asked him what he though of restoration on antique silver. He said, "Depends how good the restoration is."