The symptoms you're looking for are vomiting, inappetence, lethargy, and/or abdominal pain.
The vet tech side of me will tell you yes, corn cob ingestion is a big deal and frequently leads to a foreign body requiring surgery. The dog owner side of me says, "#*%*+~!, even though I'm fully aware and try my hardest to prevent it, my stupid $&#%^ dog has still managed to eat SIX corn cobs over the years because he works in tandem with the @/}**% cat to get them off the kitchen counter!" And he's been fine every single time. Then again, he's a hundred pounds and he chews them first before swallowing them.
That's really what it comes down to -- the dog's size as compared to the size of the pieces he eats. If you were to call your vet now, they're going to tell you to monitor for the above symptoms. They won't be able to tell you if it's going to be a problem until it's a problem. It's one of those things you have to wait and see.