Smooth trigger

While looking over a couple 1917s I noticed one does not have serrations on the trigger. All I've ever seen have vertical serrations. Any ideas?

I believe the smooth triggers are WWII replacement parts.

I think I've seen an "E" or "R" marked smooth trigger. Maybe both.

You will find all three makers put out smooth and serrated triggers, there were NO WWII replacement triggers.

My guess is early ones had serrated triggers and they went smooth to speed up manufacture time, just a guess though.

Dan