A common ploy used in card making during the 60's and 70's was to take a picture of the player w/out a cap on, so you can use it if he's traded and there wasn't an opportunity to get an updated photo. Since most photos were taken during spring training or the previous season in NYC there were a lot of players who wound up on new teams without updated photos. If their new team had a totally different color scheme performing an airbrush job on the cap and uni were just not feasible. The fallback would be to use a capless headshot that was cropped very close as to reveal very little of the jersey top. This caused the "Big Head" phenomenon, which is how this style of card got the nickname "Big Head, No Hat", or simply abbreviated BHNH. Based on my numbers I found 22 BHNH cards that are needed to be fixed. In total there were about 40 of these (out of 756) that were issued in the series, but more than half of them never even played a minute for the team that they were "traded" to in the card set.
Below is an example of a BHNH card and an updated version that falls in line with the project.