I Notice That Child Developmental Milestones Are Usually Presented For

I notice that child developmental milestones are usually presented for blocks of time, 2 months, 7 months, and then for single years, 1 year and then 2 years. However when I want to look at milestones for a 3 year old, I find 3-and 4-year olds are clustered into one block "3-4." Are there other guidelines that pull apart 3s and 4s so that I can get a closer look at one of them at a time? Thank you- Ran Jarrell