The Little Gems webpage for Noah and Nelly in Skylark states that there are only 15 episodes of the series, as does the wikipedia page for the same series. However according to the Radio Times archives made available by the BBC in their new Genome project there were in fact 29 episodes, as follows:
1. A Savings Week
2. The Time We Were There
3. Tea
4. A Long Time Ago
5. A Stay At Reservoir Desert
6. Something And Nothing
7. A Smashing Time
8. A Damp Spell
9. A Steam Up
10. A Flower Show
11. A Wail Of A Time
12. A Sweepstake
13. A Very Funny Day
14. A Visit To The Theatre
15. One Afternoon
16. A Picnic
17. A Frame-Up
18. A Journey Abroad
19. A Splashing Time
20. A Wild Day
21. A Jumpy Time
22. A Quiet Time
23. A String Of Events
24. A Reading Lesson
25. A Very High Flight
26. Lunch
27. A Stay At Clockwork Canyon
28. A Fishing Holiday
29. A Seasonal Time