"Interesting hypothesis on the side gussets, but they don't appear to have been a part of a shoulder strap. I gave the bag a closer inspection this evening and found the one remaining complete gusset is a little over an inch wide at the widest, but it tapers down to about 1/4" wide and ends at the top of the bag."
I have been wrong before, and will be in the future. Apparently I am pretty skilled at being wrong. :-) Thank you for the additional photos and descriptions. God Bless, Marc