“Sheet music on music stands provide the road map for an orchestra’s performance, but scribbled annotations by the players impose a conductor’s ideas and serve as simple reminders to make an entrance or count correctly. Now, with more than half-million new digitized pages poured into the New York Philharmonic’s electronic archives, that world is open to inspection. It may prove interesting to concertgoers, and fascinating to musicians who may have to play those parts themselves. The Philharmonic on Thursday said it had completed the first phase of an effort to put its vast archive on the Internet. Lasting three years so far, the project has made available public programs, scores and internal documents from 1943, when Leonard Bernstein made his debut with the orchestra, to 1970, the year after he left as music director.