[Vwdiesel] vw 068 103 373M cylinder head

[ken1]

I would like someone to tell me the significance of the following info displayed on a couple of 1/6L heads that I have seen. 
One head has the part number of 068 103 373M. Each of the prechamber cups have a dot or peen mark at about 8 o'clock.

The other head, 068 103 373E, has a peened/punch mark on the head on each side of the prechamber cup at 9 o'clock and 3 o'clock.

I have not been able to check other heads, but I found on another head, 068 103 373M that when I put a magnet on the base of the exhaust valve and got no attraction, but when I touched the magnet to the intake valve, it was attracted. Does this mean that the exhaust valve is a non-magnetic alloy or that the valve is sodium filled?
ken