It took the BSA almost two decades to release a handbook for patrol leaders. And there have been two periods since then (20 years total) when there was no Patrol Leader Handbook, the BSA instead offering a much more general troop leadership guide. The covers of all youth leadership books are shown below, including all Patrol Leader Handbooks, the two troop leadership books, and the recent Senior Patrol Leader Handbook.
Handbook for Patrol Leaders, First Edition, printings 1-4, 1929-35 (left)
Handbook for Patrol Leaders, First Edition, printings 5-18, 1935-50 (middle)
Handbook for Patrol Leaders, First Edition, printings 19-34 (somewhat revised), 1950-67 (right)
Patrol and Troop Leadership, 1972-80
There was no handbook specifically for patrol leaders during this period, only this much more general leadership book with limited information on how to run a good patrol.
The Patrol Leader Handbook, Fourth Edition, 2002-present (left)
The Senior Patrol Leader Handbook, 2002-present (right)
These books are spiral-bound, which lets them be conveniently folded flat and avoids the problem of pages falling out of a well-used book. The Senior Patrol Leader Handbook is the first leadership manual specifically for the SPL.