If it can be verified definitively through the vin stamp, then there is no deception with the DZ stamp, they simply replaced what was already there. On the flip side others would still complain if there were no stamp at all so you can't win either way. However, with the documention of what was done, the rebuild that included decking, all disclosure, then there really shouldn't be an issue. The vin stamp proves it's legitimacy. In this case, on top of all that, things were also verified with Jerry McNeish, whom some consider the last word, or at least good reassurance of what you're buying.
Without the vin stamp at the oil filter obviously that changes the whole perspective. In this case, December and onward for 69 Norwood cars, it's a benefit making it easier to document. We don't necessarily have to weigh everything solely on that engine pad stamp. I agree, nice to have, but......