Remember back to a time when you used to scour your collection to try and find those "rare" error cards? Errors that were caught very early by the manufacturers could be worth hundreds of times more than their corrected counterparts. For example, Mike Krushelnyski's 90-91 Pro Set card is hardly worth the paper it is printed on. However, his error card, that is a completely different story. There are none of them for sale on eBay as of now, but I have seen some in the past listed for well over $50 dollars which is a fair bit more than the book value of 5 cents for the corrected version.
Other errors are very common and sometimes the errors are never corrected. Recently I was thumbing through rookies and I gave Reggie Lemelin's an extra close look.
1981-82 OPC Rejean Lemelin Rookie
If you happen to have a Reggie Lemelin rookie and a free moment, take a look. I am curious if OPC ever caught the error and fixed it or if it remained as a typo for all to observe.