I don't have a complete sheet in my archives. 1959 Indians and 1960 Baseball were 80 card sets (with 1 pulled in 1960) also and don't seem to have SP's. I did not believe there to be SP's while building the Williams set (beyond the pulled card, which is much more common than its price suggests). The POP report doesn't indicate to me that there are patterns of DP's or SP's (
https://www.psacard.com/pop/baseball...williams/37470). I would think 1 card was probably DP'd for part of the print run, to get an extra card out of a sheet when they pulled #68. But opinions don't mean much.