If the actual speed traveled is not stated on the ticket in the relevant box is it still a valid document?
The speeding ticket is just an offer to get the matter over and done with without the need for a court hearing. If you do not accept that you were speeding then you should reject the fixed penalty ticket and ask for a court hearing. At court the officer will attend and give evidence to try and show that you were speeding.
If you cannot cast a doubt on his speeding allegation then you will be convicted and you will face higher fines and court costs. If you can cast a doubt then you will be found not guilty.
Have you got any points already? Are you a new driver? Tell me more. What speed did the officer alleged?