I still have my doubts about the inlay.
Look at the parts that I have marked.
There is pitting in the brass ? there is pitting on the edge of the iron/steel and the brass. Where have you ever seen that iron and brass are showing the exact sort of corrosion.
Also the file marks, they go smoothly from the iron into the brass.
Alao the shape of the inlay does not make sense.
I still go for varnish or glue remains.
Best regards,
Willem