I own 1000s of pieces of gas pump literature and I have read most of it, but I have never found anything, or any company, that answers this type of question.
Sometimes I think it had to do with the temperature outside the day they made the pump.
If you have my gas pump book, you will notice that I have been able to identify three versions of the 176.
I just revised the 176 etc. page on my website, adding much more literature, take a look at the pictures, maybe you can come up with the answer. http://petrolianacollectibles.com/gb%20176.htm