I would say just write something up in your birth plan that says you're using NH and that you might appear to be not as far along as you really are, and a brief explanation of any specific techniques that you plan to use that you feel like might need some explanation. To be honest, I included the data sheet thing in my notes with my birth plan and I really doubt the midwives bothered to read it. They did read my birth plan though and did a good job of respecting my wishes as I laid out in there, so I think that's probably the most important place to include anything specific. Really, the main thing for me was letting them know it might appear that I'm coping well and not as far along as I really am and that it's important that they do what they need to do (as far as checks/monitoring) while still respecting my birth space and the atmosphere I created and not interfering too much with me just getting on with it and using the techniques as I'd practiced them. They did this and I don't think the data sheet itself was all that important.
I will say, I definitely didn't appear to be far along in labour when I really was, so I think mentioning that to them is really important. They didn't think I was in especially active labour because I was just breathing and not making a noise and seemed really in control and relaxed. It wasn't until they'd been there long enough to realize the contractions were coming really close together and I was getting pushy that they asked if they could check me. Turns out I was already fully dilated and pushing! I don't think they would have guessed I was, so it was important that they understood to anticipate I might be just coping well with the pain.
xx
