[Milsurplus] ?? on Contract Date

[Hue Miller]

Navy model DU.  NOT DU-1. 
Manual sez:

"Manufactured for 
U. S. NAVY DEPARTMENT
BUREAU OF ENGINEERING
Contract NOs-59120 
Dated February 12, 1938.
by 
BENDIX RADIO CORPORATION
Baltimore, Maryland
I.B. 121                          October 1939"

I assume "I.B." means "Instruction Book"
The manual sez it's for serials 1 - 215, so the manual 
is for the first production. 
Why the long time between the contract 
date and manual publication? Am i safe to assume
the manual's 1939 date is the same as the appearance
(actual manufacture) of the equipment, or maybe a 
prelim manual appeared earlier? -Hue Miller