I am not sure if I can give you the answer you are looking for... but I can tell you about my experience with CP. My little one was a twenty six weeker born weighing one pound eleven ounces. She only had a grade one IVH. With only a few bumps in the road, her NICU stay went well. She came home and the doctors predicted she would catch up quickly and easily.
She was home for a few months when I knew something was wrong. Since she did well in the NICU, no one had talked to us about CP. At six months old (actual) my baby hardly moved on her own. I
I brought it up to the pediatrician and asked, "Do you think it's CP?" She said, "I think so but it's not my specialty. Let's wait and see what the specialist says."
Like Lindsay said, there were so many questions. What does this mean for us? Do we need to plan for a wheel chair?
As you've noted, they don't diagnose CP until babies are older. The specialist asked me, "What do you want me to do now?" I had read that early help makes a big difference. But, I didn't know how to help my baby. I said, "Tell me how we can help her right now." He prescribed PT, OT, and eventually speech. I also enrolled her in weekly music therapy.
Within a few months, it was like a light switch had been flipped. She started to move. At the age of 18 months, she received her diagnosis of CP. She is almost three now. Most people can't tell that she has CP. One really has to look at the quality of her movements, the overflow, feel her tone, or notice her AFOs or SMOs (which she needs time to time while she grows) to notice that she has CP.
She is speech delayed, feeding delayed, and fine motor delayed. Socially and cognitively she is ahead of her peers.
I guess what I'm trying to say is that CP can mean A LOT of things. Every baby is different.
Has it been easy? No. We have put in a great deal of work, love, hope, and mileage on our car. Has it been worth it? Absolutely.
Good luck to you. I hope I've answered at least a tiny bit of what you wanted to know.