I can't speak to most of this stuff, but my son was diagnosed at 2.5 with receptive expressive language disorder due to having higher expressive than receptive language. He scored at 4.5 for expressive and around 3.5 for receptive. It was very hard to understand how being ahead in both could be a disorder, but it definitely made him different from other kids. He did not understand more than he said, he understood exactly what he was able to say, maybe less? It didn't really change much since now at age 5 we talk to him like an adult and he responds at the same level. My son does have disabilities (ASD, possible ADHD, probable etc.) and we find out in the coming week if he is in fact 2e, but just thought I'd chime in with our experience with odd language development.
