The BSA had a Scout Handbook their first year of operation, and released the first Scoutmaster Handbook in 1914.
Handbook for Scout Masters, First Edition, 1914-1920 (hard cover)
All printings included hardbound copies, and some also included leatherbound. Apparently there were no paperback copies. All printings refer to the position as Scout Master (two words).
Handbook for Scoutmasters, Second Edition, 1920-36 (leather cover)
All printings included leatherbound copies, and some include a loose-leaf version. Leather covers came in several colors, especially black, but also maroon and green. By now, the position is called Scoutmaster (one word), though early printings use both terms.
Handbook for Scoutmasters, Third Edition, 1936-47, all hardbound
This edition was issued in two volumes with identical covers (except that the spine indicated VOL. 1 or VOL. 2). Printings of the two volumes were typically printed several months apart rather than simultaneously. Volume 1 covers administrative and general how-to information, while volume 2 contains more program-oriented information.
Handbook for Scoutmasters, Fourth Edition, 1947-59, all soft cover
The first six printings (left picture) showed everyone in traditional campaign hats. From the seventh printing (1953) on, everyone is wearing overseas caps.
The Official Scoutmaster Handbook, Seventh Edition, 1981-90, all soft cover
Cover is the 1981 Joseph Csatari painting "After Hours" (Csatari paintings also appeared on the covers of the Scout Handbook and Patrol Leader Handbook during this time frame).
The Scoutmaster Handbook, Eighth Edition, 1990-98, all soft cover
This excessively posed color photograph is the first cover photo since the First Edition. This is the last Scoutmaster Handbook that is a true book (that is, bound).
The Scoutmaster Handbook, Ninth Edition, 1998-2015, all loose-leaf
It's a stretch to call this edition a "handbook". At 8.5x11" in size, unbound, and three-hole punched for placement in a bulky ring binder, it is hardly handy, and totally unsuitable for use in the field. This is undoubtedly much cheaper than publishing a bound book.
Troop Leader Guidebook [new title, but equivalent to a 10th Edition of the Scoutmaster Handbook], 2015/16-????
New, expensive, 2-volume handbook (volume 1 released July, 2015, volume 2 to be released sometime in early 2016). This is also a large, unbound 'book' intended for placement in a 3-ring binder.