Remember that Swiss watchmaking of the period was something of a cottage industry, with innumerable parts suppliers feeding a much smaller number of manufacturers, who would be responsible for the final assembly into a watch.

For some Zodiacs, it's pretty much impossible for even the most devout brand loyalist to deny that they were made by Heuer:

The model references are the same, and the serial numbers fit perfectly into batches of Heuer-branded watches.

For those that are less clearly derived from a Heuer, the picture is less clear. There was obviously an amicable relationship between the two companies for the watches above to exist, so it's no great jump to think that Heuer may have given its blessing for its parts suppliers to make available things like fluted pushers to Zodiac.