I wouldn't worry about it. Back on motors that had offset keys for adjusting such, four degrees was the first level of adjustment.
The adjustment was 4,6,8, and 10 degrees with one tooth being 18 degrees. Thus any value could be achieved by either advancing or retarding the cams in these increments or jumping the chain.
Proper evaluation in this area can not be done with the marks. It must be done with a dial indicator on the valve in question using the TDC specs found in the TDM (tech data manual).
Bosch Master, ASE Master, L1
33 years MB technician