Re: Fathers...Know your kids baseball card collection??
The 1962 set included cards which had a light - but noticable - green tint. Those cards were later corrected.
The 1069 set included a lot of cards which had minor errors such as background color or letter coloring - again, those cards were corrected.
As for cards which dropped in value, one of the most extreme instances is the 1990 Score "Black and White" Bo Jackson. It depicted Bo in his football shoulder pads, a baseball bat over his shoulders.
Early on, the Score set was hard to get, and the card was in great demand. Some were paying more than $30 for that card.
Around July or so, Score mass produced the card - big time. By September, the card could be had for less than a dollar from reputable dealers.