The look-up algorithm gets stumped on the 'a' for box 150a. I can't find anything in that box. Even on a direct address to the file, the 'a' got lost, i.e.,levysheetmusic.mse.jhu.edu/cgi-bin/display.pl?record=150a.018.001&pages=4
turned up that in Box 150, item 018, page 1, not that in Box 150a.
click here