When you book in, you let them know your due date and they put you I with people who are due at a similar time. If you’re worried about booking too soon, you could book after your 20wk scan. Perhaps contact your local nct to see if they often book up early or if there’ll be spaces to book in a month or so
The company I booked ours with gives you an indicator as to which due date matches the course so should I would imagine they’re all the same :) I’m due mid Jan and it recommended end of Nov start date.
I wouldn't really rush at this stage. I checked them at gone 20 weeks and the courses still had loads of space on loads of locations! I didn't end up booking any NCT though. 300 quid was just too much! I just went to the one free antenatal provided by the midwife office!
My first was due in June and our classes were in May. As for NCT classes themselves - on the plus side, I still keep in touch with some of the other mums 2+ years later. When we were on mat leave we used to meet up quite often which was really nice. On the minus side, I don't feel like I learned anything particularly useful there. For me, the only value was meeting people x