To everyone 
Let me introduce myself  I am  Mr Sicuro partner of Sicuro Publishing  company that has  copyright register of hundreds  WW II reference and data 
I am very surprise  that you are interested in Our WORK and I underline OUR work  .. 
I would like to give a short explanation to everyone interested in this subject ..  ( " I am not intention to patronize or to be exhaustive " )
Let start ..
I suppose that somebody has bought in the past a REPRINT of OLD book... and has never question himself about ownership copyright etc ..
No one question himself when buy Classic Music  or Marilin Moore Picture on Book or magazine etc. 
Nowadays the web has give possibility to do deeply search in we love the most ... that it is great  for everyone  .. freedom is Knowledge 
To make the Long Story short ..
Any Publisher before .. PUBLISHING any work has to acquire and register COPYRIGHT .. 
If  Publish a book  acquire copyright from author in lieu of  Author Royalty ... and  other .. possible author agreement right ..
IF the Publisher  has to or want to publishing a former work that has not Author and refer to a " Product Manufactured  and not in production any more " .. has to do similar procedures
Manual are instruction books refer to particular model and version and etc.
The Right of Manual ended when Product is not manufacture anymore 
Even  The Manufacture is still in business them  .. have not " Legal Title any More as well do not have any liability  about the Old Product "...
Liability and Copyright are strongly relate  in this matter  Company that do not support a product manufactured from them Loose  the right of Product 
Because of  etc etc. .... 
I can ad a compete Legal Literature  Reference...  very Boring and  very effectiveness  in CLEAR  this issue .. 
This issue was work out from US Government in Cooperation with UK and France Government .. refer to OIL industry in early 60 ..  
By the way refer to Machinery for Oil extraction...
Bottom Line  ...  Publisher has to copyright his own work if want Publisher 
Manuals and other Instruction Book ( Military in Special case ) of product that are not any more manufactured Or no any more supported from Manufacture...  do not have the right of Manufacture any more..
Moreover  any product that change format , and has  assembled information from former copyright work , has " Collective copyright " etc. etc ..
Please  I suggest to speak with  legal advisory  if you want  a better understanding 
I  understand that you can be surprise  but what we have done  is what every publish has to do for " Law "  . copyright  OUR work ..
Some one can argue that this work is not OUR work ..
The Answer  is You are wrong  Sir  
TITLE and Subject are 
Same of ORIGINAL work Done 
Contents and FORMAT 
are NOT  like Original 
Furthermore I suggest to read carefully what we have register and   What does mean " Collective Copyright Work "
We appreciate your interested 
Sincerely
F Sicuro
http://www.sicuropublishing.com/servlet/StoreFront