Rock Island 1903 NS Bolt?

Help please. I was going through a relative's gun parts and found a nice looking 03 bolt body that had an NS stamped on the top of the safety lug and the letter "A" under the bolt root. My limited research told me that this might be a Rock Island bolt made in the 20's. No other letters are present. What is strange is that the bolt has grooves, one in front and one behind the safety lug. Looks like the front one was for the back of the extractor to ride in but no idea what the rear groove would be for. The relative didn't want to shoot it and just threw it in his parts box. I wish I had my camera phone with me when I saw it, but it was home charging. Any idea wha the grooves were for and if this is a Rock Island bolt indeed?
Thanks!

It is a Rock Island bolt, ca 1919.

Your description is not consistent with a Rock Island NS bolt. You describe a blend of features that appear on three different bolts. So I am unable to distinguish which one you have.

Hope this helps.

J.B.