It is my understanding that "leveling off" is referring to the fact that some kids will revert to the mean, even if they picked up on some things earlier than usual. I imagine it originated from the fact that in normally developing kids, maybe all kids, there are spurts in different areas. E.g., some kids may pick up on reading faster. So, perhaps some ND kids do level off at some point around third grade, as the myth goes. But the leveling off concept doesn't seem to apply to GT kids.
My DD is still very much GT, but her early development (very much like the OP's daughter) doesn't fully line up with her current development, assuming you were to go whole-hog and predict IQ from her development at say, age 1. She looked more extreme as a young toddler. I think her IQ results may not fully represent her, but I would still maintain that there is no way she is PG, despite looking kinda PG at that age.
It's not that I think she "leveled off," exactly. But I do think toddler development is not always a clear indicator. Toddlers are weird. I feel like I had a better picture of who she was by about age 4 or 5. Meanwhile, my DS is 3 and looking more gifted by the day despite being much less of a shocker at age 1.
