Complex sentence: For more than three decades from its inception in 1932, many New Yorkers called the entire IND system the Eighth Avenue Subway; though it was the first "portion" of the IND put into service, this was never its official name.
Split into simpler sentences: For more than three decades from its inception in 1932, many New Yorkers called the entire IND system the Eighth Avenue Subway. Although it was the first "portion" of the IND put into service, this was never its official name.