Indeed, it is normal for that model. The American made version of the M9A1 doesn't have that extra indentation around the firing pin hole. The one I had before the great FTF boating accident, looked the same as your pic and it functioned/fired normally.
"There is no hunting like the hunting of man, and those who have hunted armed men long enough and liked it, never care for anything else thereafter." - Hemingway
“The greatest ignorance is to reject something you know nothing about.”