what type soil did you grow them in and how did fertilize them

Hard to know what possible issues other than how much actual sunlight, or spacing.

The 75 days claim seems to be based on 75 days from transplant, but then over 100 days then should be enough to get some size. Maybe start seeds a little earlier so they have more time to grow roots before the heat of Summer.

Everything around it did fine and so did my other leeks, I planted them in 3 places with the same results. It was definitely later than I could have planted them and I will plant them earlier.

I was also guessing maybe from transplant but nevre read that anywhere. I figured at most add 25 days (33% more). 100 days from when they came out of the soil (June 1) is mid September. They were still smaller than a pencil at the end of Sept.

I am mostly curious if others have had success with that exact leek.