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Tom,
The purpose of witness marks are just that to witness something. A true machinist can tell you what they are for and they usually line up. I don't dispute Bob's explanation but I certainly wonder about it being correct! What purpose would the marks have if not to indicate the relative position of the barrel and receiver? Does your barrel have the land diameter digits?
It is unusual to find the serial number suffix on a Mauser military luger barrel, as a matter of fact I don't think I have any that does!

Regards,

I am a man of much wisdom acquired through the years as the water flowed in the river.
My wisdom is based on my need to know in my world.
I have no knowledge of your world.
I will leave this earth with that peace.
My Wisdom Is Mine. (Gertrude)