There is a lot of excellent information in the technical manual section of this web site that, using your vin number, will help you identify the month that your car was produced.
There are many late production 230 SLs that were registered as 1967 models (at least in the US).
Your data cards can also provide a lot of information. If you don't happen to have your data cards I would suggest that you contact the Mercedes Classic Center, with your VIN number in hand, and request copies.
Norm