I can't make out his clip.
Both my early SJ March cars (one is a parts car, the other in my sig) have this clip here and under the car to hold the gas gauge wire.
Maybe part of the confusion - different results is that your comparing cars from different production periods and for details it can be like comparing details from other years or even plants and expecting to get the same results or findings
Here are some examples from Nov- Jan 67 built at San Jose. Found dozens of examples of these clips being used during this period rather than the later retainers. Change over is in the 158xx-162xxx VIN range. Of course it would be a soft range since we know that cars were not built in sequential order and we don't know the real build dates of all the cars in the survey
Ignore the arrow - picture was originally uploaded for another discussion about the fuel wire retaining tape locations
Clip style IMHO has nothing to do with body type in my review
You will likely find more with the rubber covered metal clips on cars at show since they are easy to purchase and find - rather than all being found with that clip prior to restoration