Band Leaders was began in or around 1942 and featured articles about the band leaders, naturally, as well as the band, singers and music of the era. In the first years, the magazine was quarterly. In 1944 and 1945, publication was bi-monthly. Starting in 1946 it was published every month.
Around August, 1946 it became "Band Leaders & Record Review"
We assume that "bi-monthly" in this case means "every other month".