Re: History of the Forklift
Got to be careful with the terminology. If that figure included "powered industrial trucks" of all types, it also includes the tractors designed to tow trains of carts as used by the post office and express companies. One common brand of fork lift trucks during the fifties was Tow Motor, which should give some hint as to the origins of the product line.
These tractors are noted in John A. Droege's "Freight Terminals & Trains" was first published in 1912 and again in 1925. Chapter Twelve, the Mechanical Handling of Merchandise Freight, includes references to electric freight trucks used within large freight terminals. I've frequently consulted this book for freight operations details.
The NMRA reprinted the 1925 edition in 1998. New copies are available through the NMRA Store. A number of used versions are available through booksellers.
The 1912 edition is available to read and/or download through Open Library. Chapter Twelve starts on page 327.
Google Books has the 1925 edition to read or download.
I did not see a specific reference to fork lift trucks.