I only remember because of events coinciding with what they did - eg DS1 was sorting by colour on his first birthday, because he was given a stacking toy with different coloured rings on different posts and he put them all on correctly, and my SIL commented on it. I remember it was Easter when he started using colour names. He also showed us that Easter holiday that he was reading numbers (off houses, buses etc).
For DS2 I remember he started telling me the colours of the traffic lights when we were driving to hospital for him to be admitted with severe asthma. So I can date that.
There are lots of things I don't remember though - eg how long potty training took.