It means it is a different run environment than normal weeks. It does not mean that players whose card is from the '60s will play better.
In 1961, according to
this sheet, there are more balls in play, the same amount of homers, more triples, fewer doubles, slightly more walks, fewer strikeouts, and a similar slash line to the accepted 2010 baseline for regular league play.
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OOTP's Official Perfect Team Hype Man / host of TWIPT Saturday Showdown and Perfect League World Series
"Find a way to be alone in a baseball stadium at sunrise, when the only sound you hear are about nine birds that got lost, and found themselves in a stadium, and they’re chirping across the grandstand trying to figure out where the f*** they ended up." -Dan Besbris
