I believe in that era teams had official nicknames and alternative but more popular commonly-used nicknames...or no official nickname and a bunch of commonly used nicknames. 1913 was likely the year the name 'Yankees' became official but it had been used for several years prior, thus explaining why it was on a 1911 baseball card.
Even more confusing is the history of the Dodgers team name...they had a host of various commonly-used nicknames before Dodgers became official (for example, the Superbas) and the history of when one name began and the others ended is murky.
Particularly convoluted is the history of baseball in Washington. Everyone is surprised to find out that even the Washington Senators of the 1900s - 1950s were officially known as the Washington Nationals even though they ceased being referred to as the Nationals around the turn of the century. The Nationals name currently used has a longer and more official, arguably, lineage than the Senators moniker.
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