I’m familiar with Royal thank you, used them too.
As to the rest of your post as a pre-computer age typist, secretary and clerk....BS.
You did not put a form aside and work on it at a later date on a different typewriter in the same office. Once you put a form into the typwriter you finished it. Difficult to get the lines even and lined up otherwise, tedious business, and a headache to boot. No secretary/clerk/typist worth her salt would have done this. NOONE. You might not have finished all the forms in your stack on the same day....but you definitely would NEVER have stopped in the MIDDLE of one, then moved it to another typewriter, even IF there were another brand of typewriter in the same office. That is so much bunk I’m doubled over laughing.
The rubber stamp - okay - but its not the rubber stamp parts of the LFBC that in dispute here. Try again.
Some analysts detect a commonality in the tab settings ~ which isn't terribly critical, but it does mean the typewriters in question were used EXCLUSIVELY in this process.
Different things happen on different days and the forms went into and out of platens several times.
You can buy off on that or not but over the years I designed or redesigned over 1,000 federal government forms, all of which were put into use by the general public, or for specific government purposes.
To do that job successfully I had to imagine every single detail of normal use ~ and supplement that with on-site field observations of people using models of the form under design, or its predecessor(s).