Autos dont have "stages" in the same way that photo period plants have stages. Most autos are so quick that there is no need to cater to a certain stage. Seedling, veg and preflower are basically rolled into one.. Most autos show sex by day 21. So that first 30 days or so would be considered your seedling, veg stage and preflower stages.. Once it shows sex, it on to stretch and preflower. Which only lasts a week or so. From there you should be in early flower by week 4-5..
There aren't many (if any) nutrient lines that are made for autos, or with autos in mind. Their feed recommendation are commonly based on photoperiods, with 4 weeks of veg and 8 weeks of flower. 4 weeks of an auto and you could be in preflower already. So basically all of the "stages" of an auto happen without warning, one after the other, and usually all with the first 30 days of life.