For some reason Citizen didn’t give model numbers (i.e. 67-xxxx) to two of their chronographs. One is in the 8100 line, and carries the case number 4-900014. There were two versions and I’ve managed to acquire one of them:
This one was made in May, 1972:
I’ve added a pic of this one to the article – https://sweep-hand.org/citizens-vintage-chronographs/ – where you can also see the other type which has a silver sub-dial.
The other model without a model number is a colourful Challenge Timer, more usually called a ‘bullhead’ these days. This is the 4-901096: