As someone said in a previous post, if you caused an application to go into a second reel of tape, you just increased the processing time significantly. Reruns due to hand crossing was not an unusual occurrence. Disk drives were not commonly used for data file storage until the seventies in most shops. Tape sorts took a LONG time. Multiple reels of input only made them longer.
Tape drives read and wrote in only one direction.
A tape sort took many passes. You had to have several tape drives to do a sort. At 556 BPI in the sixties, you did not get much on a tape. The tape drives had to be cleaned several times a shift. Sort failure due to tape error happened.