If you need reference for how good Bob Gibson was, they had to change the rules and lower the mound because Bob Gibson was so good, nobody could hit him. Gibson is one of the top pitchers in the history of the modern era and his rookie card came at a time of large scale discrepancies with card quality.
For those not aware, baseball cards aren’t printed individually at their size as found in packs. They are printed with around 100 other cards on a large printing sheet, then cut down using industrial equipment. Quality control wasn’t as big of an issue then, and it led to many off center cuts, affecting the overall look of the card. That, combined with the card being 61 years old means that very few of these cards can be found in a high grade, making centered cards with good corners incredibly desirable.
Random Bob Gibson fact: Gibson won the Cy Young in 1968 with a 1.12 ERA. That is the lowest ERA all time for a starting pitcher who won the award. Only Rollie Fingers had a lower ERA, with 1.08 in 1981 coming out of the bullpen for the Milwaukee Brewers.