I'm glad to find so much company! My situation is a bit different, though. I didn't come on the scene until DS was 2, and we didn't join the family under one roof until he was 6, so that's where my day-to-day experience really began.
Also, while we knew he was smart, and spoke articulately and had a large vocabulary from a very young age, we never thought "gifted" until we saw (to our horror) what passed for first grade curriculum.
So, yes, my reading of the 5 levels is quite sketchy. I would find it so much more helpful if older-age milestones were included as well. Still, I find it valuable as a reminder when I have those "maybe I was wrong" moments.