Frankly, I think there was also a change in the compression ratio, which was never made official or public. Many "late" heads do not show the compression ratio anymore, but some, for some markets do. The head on my car shows 9.0:1 instead of 9.3:1.
There was a "low compression" option, which my car does not have. It is a regular German spec car, built in late November 1970.