It is probably just the early 1970s poor photo editing. Could also be the effect of the "green screen" technology of the day to separate the player's image from the plain backdrop they used. If they didn't photograph in front of a special blue or green screen they probably used just a plain white backdrop.
We would need to see the specific card you are talking about and compare it to other scans of the same card to know for certain if it was part of the printing process or as you said a previous owner embelishment.
I collect: Baseball, Football, Hockey, Mostly Vintage pre1980, My Homie teams - Washington/Baltimore Teams Senators (Twins, Rangers), Expos/Nationals, Redskins, Capitals, Bullets/Wizards - HOFers - Non-sport (mostly TV shows and movies).
My Trade List is very much a work in progress
CaptKirk42s Trading Card Blog Curly W Cards Strive For '65 YouTube klandersen42