Greg, I believe the Diamond D stamp is original. When an N386(Boxer or actress) has an advertisement on front(Echo for your copy) I have never seen one without the Diamond D stamp. When they don't have an advertisement on front they always have the Spaulding & Merrick writing on the reverse. I could be wrong but I haven't seen an example fit outside of what I listed above but you are much better than I am at this investigative stuff.
Attached is an example of the pattern with multiple sub issues:
https://flickr.com/photos/201243808@...7720319623563/
https://flickr.com/photos/201243808@...77720319623563